Random (evil) Network Reset

Start the Windows XP (SP1) box up, d-link wireless card finds d-link router and automatically connects to network.

WHAT HAPPENS
Surf two pages in IE (or Mozilla), or attempt to download anything (new virus definitions), and TCP/IP settings get changed to: 169.254.35.49, cutting my connection. Manually changing the settings back doesn't seem to help--only a full restart will replace the 169 address with a 198 address.

WHAT I'VE TRIED SO FAR
I have no idea where this 169 address is coming from. I thought it might be spyware (my son had downloaded tons of spyware-plagued crap) and ran spybot, which found and fixed many problems but not this one. I also installed browser hijack blaster and ran it while I surfed to see if it would catch the reset. It didn't. I've run my anti-virus software, but it doesn't have the latest virus definitions on it because I can't download them due to this resetting problem, and I can't run trend micro because the network connection gets reset before it can finish scanning. Switching from IE to Mozilla didn't work either.

I have two other wireless boxes that work fine so I don't think I'm picking someone else's wireless signal.

Any ideas?