Umm, you are either missing important things (ethernet card driver etc) from the kernel configuration, or including them as modules (if so you need to modprobe them to get them to work) and not loading the modules. You can add lines such as:
to rc.modules to load modules. Actually, rc.modules should be full of such lines, most of them commented out, and some of them (that you want to be loaded) uncommented.
For your networking, if you can paste your 'ifconfig' and 'dmesg' (only parts relevant to networking) output here, we can try to see what is wrong. But I am pretty sure that it is due to missing things in your kernel. I'd advise you to play with your kernel configuration a bit and recompile. Be sure to include important things (ethernet card drivers!), and build them right into the kernel (not as modules) so that you don't need to worry with modprobe's. Here is a procedure that may come handy:
Boot your 2.4 kernel, run 'lsmod' and write down all the module names.
Next, boot your 2.6 kernel, and run
for each module you have written down (and is missing from 'lsmod' in 2.6)
See if this works. If it gives you a FATAL line, and the module turns out to be something important (ethernet card driver
) you need to go back and recompile your kernel with that included.