I have a similar problem, except all of my clients drop at the same time and my pc loses connection with the router. I have to completely reboot to get back online. That solves the issue for about 1 to 3 hours. It seems random but anywhere between 30 minutes to 4 hours i always totally dc. It makes instances a real pain at times. I usually end up rebooting 4+ times a night
I run vista 64 and I swear this problem just started within the last few weeks (hard for me to remember exactly when).
I turned on the port forwarding, turned off vista's ability to sleep the router, and also changed some flag in the command prompt to disable vista being able to cut the connection due to large packet and data transfer. None of it seemed to make any difference. I tried updating the firmware on the router but it's already up to date. It's a 2wire that was given to me by AT&T (our dsl provider). All my other pcs stay online and work fine but this new vista machine just totally disconnects without any explanation.
I've only had it happen while 5 boxing wows (software). I used to run 5 wows on this machine with xp 32 bit and this never happened either.
I tried repair on wow1 and it didn't find anything, i'll try it on wow2,3,4,5 folders later today.

any suggestions?