I have a weird problem... First, here is how I bring my modem up:
modprobe snd-atiixp-modem
slmodemd --alsa -c USA modem:1 &
wvdial

This modem works with ubuntu 5.04.
For some reason it odes not work with centOS 4.1; Suse 9.3; Slackware 10.1; Slackware 10.2 (kernel 2.6.13); Knoppix 4.0.2.

With ubuntu, wvdialconf /etc/wvdial.conf sets up modem fine and wvdial dials it without problem.

With CentOS, wvdialconf finds modem but wvdial exits with either No Carrier or No dialtone (Carrier Check = no & Stupid Mode = yes are always in conf file)

With the rest, wvdialconf can't see modem at all. kppp exits with No Carrier. In slackware ppp-go exits with No Carrier.

I have a "Disabling irq #5; boot with acpi=off" problem with all these distros except ubuntu. acpi=off does not help at all. Also tried acpi=noirq and acpi=noirq acpi=usepirqmask (something like that...), with no success.

Anyone has any ideas why this is happening?

Thanks so much for any ideas...

PS. I have a laptop (hp pavilion zv5120us)

Well... the Ubuntu kernel configuration is probably a bit different than the one in these other distros you tried. What exactly, I don't know, you wouldhave to experiment to find out what.
The hardware support is not relative to distribution but of kernel, which mean something that work in a certain distribution should work (with some configuration/tweaking sometime) in any other distributions.

slmodem driver is a bit sloppy atmo, as example, mine isn't working if the intel8x0m drivers is included into the kernel. If it's a module, everything is fine, but ALSA then can't find the "modem soundcard". It is possible ubuntu puts this into modules but other include it in their kernel. But this is just an example, in fact it could be anything, maybe an acpi problem, or maybe a kernel version problem, or maybe something totally diffrent create a conflict somewhere.
The only way to find out is to read your logfiles and to guess and experiment. If you feel safe enought, I would recommand to compile a "vanilla" kernel yourself, it would be way easier to isolate the problem doing so.

reply to: Half_Elf: Hmm.. I believe when it's configured as modules, it shows itself in lsmod right? If this is so, all the distros I cited (from Slackware to Suse & ubuntu) configure it as modules.
Could you post a c ouple of pointers on which logfiles are good to look into for this problem?
As for compiling the kernel, I did it once with Slackware, turned out to be a static one (no modules at all), but couldn/t compile anything after new kernel: I am confused about just one thing: in which folder do you issue
#make mkproper
and
#make menuconfig
commands. Also, is there a howto you know of that _specifies_ what to do _after_ compilation (with the sources and so on) so that the packages you compile later know you have an x kernel rather than a y kernel that came with the distro?
One more thing, do you know how to access the kernel configuration of ubuntu live? May be I could somehow copy it???

Yup, modules always show up in lsmod.

Since this is a hardware problem "dmesg" is probably the first place where you should start looking (just type "dmesg"), before, after and when you try to use the modem. Since this is related to pppd deamon, /var/log/syslog could also give you some useful hints.

I don't quite understand the problem you had with the slackware kernel you compiled... If you want to try to compile a new kernel, there is plenty of howto online. The general line are :
1- Download a kernel (www.kernel.org) and unpack it in /usr/src
2- Create a symlink (ln -s linux-x.y.z linux) so that /usr/src/linux point to your "new" kernel (it's how the system or packages then know which is your new kernel... it should always point to your actual kernel source, if you have any)
3- Enter the tree and configure the kernel ( "cd /usr/src/linux" then "make menuconfig" or "make xconfig" if you prefer). This is the critical step, if you forget this one, your new kernel will not have the correct options set.
4- Compile the kernel. On 2.6.X kernel, just type "make all" then "make modules_install"
5- Copy your new kernel image (from /usr/src/linux/arch/i386/boot/bzImage) somewhere ( usually /boot ) and edit your boot loader so it contains an entry about this new kernel. It is usually a bright idea to keep an entry about the old one, in case something goes wrong. Then you have to "reinstall" your boot loader on the mbr, as example if you use lilo, just type "lilo"
6- Reboot and test

The configuration file of the kernel is at "/usr/src/linux/.config". This file is the save of all your "options" so just copying this into a new kernel source directory is enought to tell "make menuconfig" what options you had. On 2.6.X kernel, you can also type "make oldconfig" before "make menuconfig" to let the make script locate the old config and try to create the new one from it. If your system doesn't have any /usr/src/linux (as most distro don't come with kernel source on default install because it is huuuge), there is usually a file in /boot named something like "config" which is a copy of "/usr/src/linux/.config".

In any case, if you want to try this, you better find a good howto on google as I skipped a lot of details.
Oh and **BIG FAT WARNING** --> Recompiling your kernel was just a suggestion, keep in mind you could (it could?) totally mess up your system doing so and it could not help at all. It is not very hard, but if you don't feel safe about it you maybe not want to try. This is some kind of disclaimer

That was a great brief kernel-compile howto! Thanks. (And thanks for the disclaimer )

I see that I was missing the 2. step all toghether and make menuconfig under /usr/src/linux-NEWSRC-VERSION. So the linux link was not changing from linux -> linux-OLDSRC-VERSION to linux -> linux-NEWSRC-VERSION...

I'll try to find the .config in ubuntu to copy it to (a new install of) Slackware. I don't think this is possible but I'll try.
PS. I am plain scared of Debian...

let alone the .config, I could not even find the kernel source of Ubuntu?????? Tried googling and searching their forum and this forum, and no sources anywehere?? It's like they did not release the sources to the public although they operate under GPL????????? Hopefully, I somehow messed up my google keyword...
Anyone with any ideas on where to find the kernel source (not through aptget) and this configuration file??? I would really appreciate the help.

Calm down, they respect the GPL, I'm pretty sure...
Most distro, especially RH-like distro doesn't install kernel source on the default install. Why? Mostly because it takes a huge amount of disk space and that they consider that their users don't need to mess in the kernel anyways (which often prove to be wrong).
I don't know Ubuntu but most of time on that kind of distribution, the kernel sources is in the optionnal packages on the installation CD, or you can download it online from their packages repository.

Thought I am surprised they didn't gave you a config file in /boot at least. Or maybe just using "make oldconfig" on a 2.6 kernel will be able to find a config file somewhere.