I just installed stable 2.6.6 kernel from www.kernel.org
Everything went fine, hwever my NIC (RTL-8139C) is detected as /dev/dev17345 instead of /dev/eth0. Therefore in system-config-network it appears as Unknown device type. I have compilled into the kernel proper drivers (not as module) and also did so for my other 3com card which works fine. I didn't use original kernel .config from Fedora because I wanted to make a custom build kernel which seems to work fine, except the RTL-8139C card.
Complling driver as module solved the problem and its now detected correctly (/dev/eth0) . Then I executed "modprobe 8139too" to install the module.