One thing you might try is to find a newer driver for your card and slipstream that onto the disc. Also go out of your way to be sure that you've not removed any networking components. Though if you followed the guide exactly as indicated, it should be okay. I still use a very similar setup for my discs, and I'm able to use a wired network connection w/ DHCP without issue.

TL;DR -- I suspect an SP3/old-ass driver conflict.