Had a problem with almost instant disconnects from WOW. System is a reasoanbly uptodate HP running vista and using a Belkin N1 wireless USB adaptor. Modem being a 2wire. I followed the blizzard solutions to disconnects and unknowns, and also tried everything in the plus.net forums, including new drivers etc. Tried a wired connection to the router and it ran fine. Tried wireless but with a different wireless connection and it still didn't work. Came to conclusion that it was an issue with the router and not vista. Swapped it for a £50 linksys model (WAG54GS) and it now works perfectly, and my wireless connection is slightly faster. No disconnects since and I have been running it for 24 hours now. For the horde !!!
Be sure to check the firmware on that thing, I had serious problems with the original firmware on one of these causing the wireless to lose it's bridge to the lan, and the ppp connection to drop - if in doubt, check with linksys.