I have exactly the same problem:
I have wired and wireless connection, and my wireles connection is being
constantly disconected after one or two hours. I have to reboot my windows
machine , rebooting my router doesn't help.
XP machine on same router doesn't disconnect.
My router is Siemens Gigaset SE555 WLAN dsl. In the begining, maybe some ten
months , my wireless connection worked just fine, and this problem started
recently. I think it started after one of the regular Vista updates.
Thank You in advance.