Having upgraded a D945GCLF2 motherboard to Debian Squeeze, I started to have lot of troubles & serious problems with the integrated network interface Realtek RTL 8111/8168.
For example, the mt-daapd music server was totally unstable, having difficulty to serve more than one Roku music player. The multicast functionality was totally broken.
After some search, it appears that the driver used by the 2.6.26 kernel for that NIC was the wrong one. Instead of using a proper r8168.ko module, the 2.6.26 kernel was using the r8169.ko module.
If your kernel is 2.6.30+, you don't need to follow this guide anymore as the kernel includes a proper driver.
If you update your kernel to 2.6.30+ and you had followed this guide before, be careful to remove the blacklist of r8169 module in /etc/modprobe.d/blacklist.conf before reboot, or you won't get any network support ...