I have Ubuntu installed for now but not for long. There are things I don't like about it. I feel limited and it doesn't feel modular enough so it has to go.
I came to decision to ditch it after installing 32-bit firefox to view flash & stuff, but then I tried to remove original 64-bit firefox and it told that ubuntu-desktop and other important bits had to go then as well! Well no. I've never heard that removing browser requires such a change and it shouldn't IMO. Ubuntus "core" programs are too integrated for my tastes.
The other thing is ubuntu splash window. When I want another GUI or no GUI at all I edit text files, so startx happens automatically with prefered gui and it's splash on launch or doesn't. Ubuntu doesn't really give me that, it gives me just Ubuntu splash where I can select different "sessions".

To sum it up, I need a distro I can BUILD instead of STRIP so it suits me. I have only five requirements:
- it won't destroy windows dual-boot on this system. very important since I work for MS for the moment.
- it's modular, easy to build more stuff on base system.
- it compiles stuff well (as freebsd).
- it's available as amd64
- internet works out-of-box

I've been thinking about Gentoo, Fedora, Debian & Slackware based on what I've read. I also have learned that some distros are based more or less on some GUI. I very much prefer "less" on that. Any ideas, suggestions?

Well, depending on how hardcore you are about having just the basics, you could go with (Beyond) Linux From Scratch. If you don't want to go that far, there's Slackware, which you can install without X11 at all. It is the epitome of stable base that you can add to. As a fedora user, I must say that it seems rather graphical for what you want. I don't think Slackware comes with a 64 bit kernel, but my experience is only 1 install on a 32 bit machine and of course you can always add it. Fedora, Gentoo and Debian definitely have the advantage in modularity (Debian has apt, Fedora has yum, Gentoo has emerge). LFS has no package manager (it lets you either add the one of your choice or compile everything from source). Slackware's package manager doesn't track dependencies for you, but isn't bad otherwise. All should configure your network correctly (except LFS which will take some work.) None should destroy Windows.

Slackware doesn't have an official 64-bit version, though there is an unofficial port for that. I'd agree that of the ones you're thinking Fedora is probably the least like what you're looking for, any of the others could be good. I'd also suggest taking a look at Arch, it also could be good for what you're wanting to do.

Gentoo supports amd64 and portage is the best package management system I ever used: It will download, configure (based on your use flags), compile and install things for you it takes care of dependencies automatically and it takes 2 sometimes 3 commands to update the entire system. It's a rolling distro (continuously updated) so you never have to reinstall because a new version comes out. You can be as stable or bleeding edge as you want (or mix the 2) and you can use any gui you want. I currently have:

kernel 2.6.18-gentoo
X.org Version 7.1.1
Xfce 4.4 Beta 2

on my iBook G4

I recommend LFS and variants for most control, but gentoo and variants for best combination of control and simplicity. Slackware's up on the list too.

Right. I'll go with the Gentoo this time! LFS isn't for me... yet. Gentoo is downloaded, md5'ed and ready to burn, but that'll wait for tomorrow.

let me know if you have any troube with the install

Yeah, I have. Well not with install, but getting it running. First I had problem with installation, but managed to get installation running by enabling noapic parameter. But now that I got it successfully installed, it stalls on the same spot as then when I tried to install it from CD. I know I should do something similar to noapic on bootparameters as well, but I don't know how to do it.

you should be able to add it to the kernel line in the bootloader config file. what bootloader did you use?

Also what you can do is setup GRUB for NT and use it to boot linux, that way you can keep the NT loader intact.

Vista is supposed to have a loader that will be able to boot linux :O

I'll believe that when I see it.