Suse 10.1 on Dell Dimension E520
Just got my Dell E520 an ran into the same problem. I downloaded the 2.6.18 kernel sources (using antoher PC of course), recompiled the kernel, and the onboard network card works fine now.
If you do not want to recompile the kernel yourself, you could wait for Suse 10.2 (scheduled dec 7th 2006) with kernel-default-188.8.131.52-23, or use Fedora Core 6 (but I didn't try FC6 yet).
Hope this helps.