xaos5 if I'm not wrong KDE only supported 2.4.X kernels and I wouldn't recommend configuring one in that "way".
You can compile stuff in your kernel directly built-in, that means, it will be a big "file" containing all you need, or built them as modules (kind of "drivers", separate files) that will be loaded later on boot process.
The reason you must have your filesystem support built-in is that the kernel when is loading doesn't know how to read your partition's filesystem (reiserfs), because the module it needs to read it is inside that filesystem that's still unknown!
I hope i didn't mix all your head, but I guess you'll get the point.
By the way, precompiled means it's already compiled, so you're actually compiling your kernel, not usinga precompiled one