hoooooow-deeee-hoooo fellas!

I have successfully downloaded slackware 8.0 quite a while ago, and installed it on my HD over a ATA100 Controller (Promise Ultra 100) using the ata100.i kernel... ok, everything was good so far...

Next I looked up the Slackware 8.0 ata100.i kernel config and modified it to my specific needs (NIC, SNDCARD, VIDCARD, and so on..), compiled it, and DID NOT WORK...

any ideas? - thanks in advance.

Yeah, i have one
You only use the kernel ata100.i but you did not copy .config file to /usr/src/linux (i dont think .config files are provided with dlackware pre compiled kernels) So when you 'modofied' your existing kernel you were actually modifying a clean kernel .config not that one of ata100.i kernel you are using, so ata100 support wasn't selected.
Now you might try to cd to /usr/src/linux and do a make oldconfig, then make menuconfig to see if make oldconfig made a .config file based on the ata100.i kernel (the one you are using)
If that doesn't work you'll have to go through a clean make menuconfig and find and enable ata100 support for yourself (together with all the other options you need) and then compile that, entirely your kernel.
Hope that helps
-NSKL