nForce4 with built-in nVidia LAN, and also PCIe Marvell LAN. I installed the drivers for both (forcedeth and Marvell), internet is working fine, it's just my Windows shares I can no longer access. It definitely used to work with 10.5.2 rev.1.

I also get the "network address must begin with afp://, smb://" etc. error message, even though that's exactly what I am typing into the box. So it seems like we're in the same boat!

Tried smbclient in a terminal, it seems to recognise my Windows box but was also unable to connect.