This is my problem. I compiled kernel 2.6 and i could not config it very well because i am a newbie, and i do not know all the preferencies of menuconfig.
Since i am gone back to 2.4.22 i have some little problems i can not fix.
First of all is my internet connection. It is very slow and if i click on its properties it is from 0 to 1 k per second.
What shoul it be?
Please help me.

Sorry that you have not provided us with more information about your internet connection, like I will assume that it is on a dial-up modem.

Look at your /dev/ttyS* and see if they have the following permissions and ownerships. (Partial listing to follow

crw-rw---- 1 root uucp 4, 64 1994-07-17 16:48 /dev/ttyS0
crw-rw---- 1 root uucp 4, 65 1994-07-17 16:48 /dev/ttyS1
crw-rw---- 1 root uucp 4, 74 1994-07-17 16:31 /dev/ttyS10
crw-rw---- 1 root uucp 4, 75 1994-07-17 16:31 /dev/ttyS11
crw-rw---- 1 root uucp 4, 76 1994-07-17 16:31 /dev/ttyS12
crw-rw---- 1 root uucp 4, 77 1994-07-17 16:31 /dev/ttyS13
crw-rw---- 1 root uucp 4, 78 1994-07-17 16:31 /dev/ttyS14
crw-rw---- 1 root uucp 4, 79 1994-07-17 16:31 /dev/ttyS15
crw-rw---- 1 root uucp 4, 80 1994-07-17 16:31 /dev/ttyS16
crw-rw---- 1 root uucp 4, 81 1994-07-17 16:31 /dev/ttyS17
crw-rw---- 1 root uucp 4, 82 1994-07-17 16:31 /dev/ttyS18
crw-rw---- 1 root uucp 4, 83 1994-07-17 16:31 /dev/ttyS19
crw-rw---- 1 root uucp 4, 66 1994-07-17 16:48 /dev/ttyS2
crw-rw---- 1 root uucp 4, 84 1994-07-17 16:31 /dev/ttyS20
crw-rw---- 1 root uucp 4, 85 1994-07-17 16:31 /dev/ttyS21
crw-rw---- 1 root uucp 4, 86 1994-07-17 16:32 /dev/ttyS22
crw-rw---- 1 root uucp 4, 87 1994-07-17 16:32 /dev/ttyS23
crw-rw---- 1 root uucp 4, 88 1994-07-17 16:32 /dev/ttyS24
crw-rw---- 1 root uucp 4, 89 1994-07-17 16:32 /dev/ttyS25
crw-rw---- 1 root uucp 4, 90 1994-07-17 16:32 /dev/ttyS26
crw-rw---- 1 root uucp 4, 91 1994-07-17 16:32 /dev/ttyS27
crw-rw---- 1 root uucp 4, 92 1994-07-17 16:32 /dev/ttyS28
crw-rw---- 1 root uucp 4, 93 1994-07-17 16:32 /dev/ttyS29
crw-rw---- 1 root uucp 4, 67 1994-07-17 16:48 /dev/ttyS3
crw-rw---- 1 root uucp 4, 94 1994-07-17 16:32 /dev/ttyS30

Else, you may have a problem with your ipV6 getting in the way.

Yes it is a dial-up modem (56kbit) connection.
The problem i can not fix is that switching back to last kernel i have the same problems of 2.6 kernel and i think this is not normal.
First of all i have to run NVIDIA driver in order to startx X, and the connection is slow although i start a root session.
(could it be a System.map and config problems?)
Thank you in advance and sorry for my dummies questions.

P.s. Where should i find informations about menuconfig options?

Your config file in /boot directory is the configuration that the kernel was built with. However, if you built the 2.6.x kernel, you may have overwritten your config file. The best thing to do is to get one from the 'kernels' directory of your installation CD.

In your /usr/src/linux-2.4.26 directory, there is a file, named '.config' (Note the dot before the name) that is the actual configuration file that is used when you build the kernel. Copying the 'config' file from /boot to this file (.config) will build the kernel and all the modules, exactly as shipped.

(OK, don't need to do that, just wee bit of info in case you want to customize the kernel, later.)

For your problem, I would suggest that you edit (as root) your /etc/hotplug/blacklist file and add 'ipv6' to it and reboot. This will prevent the ipv6 module from loading. See if that makes any difference. If not, post back here and we will continue trouble shooting....

I tried and tried everything it come in my mind, but i did not fix it.
Now i am connected with a Slackware LIVE and everything is working fine.
I think that something in pppd is the cause of my problems, so i would like to remove everything.
(Trying to compile 2.6 kernel i had to create a connection with pppconfig because it asked me the NVIDIA driver. And i think that connection is getting me this problem)
What should i do?
Is it better to reinstall all ppp packages with pkgtool? Or what else?

Reinstal ppp package(s) with pkgtool, yes.

And leave 'em in, read everything about installing/configuring/running ppp. IIRC, there have been changes to it. I am not familiar with ppp since I have not used it in about 5 or 6 years, now.