I got the same problem, lan is not working on my D520, i have installed retail snow leopard 10.6.3 with success, only the LAN was not working, so i used edp 1.8 for all LAN and other stuff.
Every things works, only the networking connection is still the problem, i don't gets the right IP with DHCP, manual works, but no internet connection.
I have done the advised max=1024 limit, but is still not working.
Do you guy's have still any ideas?