Let me start with a disclaimer: this may not be your problem! but it was mine - my NIC card was crappy. Not broken, mind you, but just crappy.
Some history: Lately, I've been getting err 7's and long, looong, freezes in-game, so much that GW was becoming unplayable. I suspected the GW servers since a) I'd run fine before, b) ping tests seemed mostly fine, and c) bandwidth speed tests were all coming up smokin' (I'm on Bellsouth DSL).
However, one night on a lark I decided to load GW onto my work laptop and run it on the same (wireless) LAN as my gaming machine and lo and behold, it ran smoothly. I then pulled the USB Wireless card out of my Tivo and plugged it into my gaming box and now I was running smooth as silk. Fortunately, I had an old D-link wireless card lying around so I pulled my generic NIC card out and replaced it with the D-Link and all my problems vanished.
Again, YMMV, but for those of you at the end of your rope (like I was), it might be worth a shot. I'd always assumed that a NIC card was a NIC card, but apparently, that's not always the case.