RT2500 Wireless Card "Losing Internet"

This is an extremely odd problem that takes a little clarity to
even describe...I'll try my best:

OK, I have a new notebook with an internal PCI Ralink RT2500
wireless card (RT2560F chip w/3.0.3.0 driver) which is accessing
my home network and the broadband modem through a Zyxel P-330W
wireless router. Everything works normally and I can access the
Internet and perform various functions simultaneously or
individually. Signal strength and S/N are excellent. At some
totally unpredictable point, I lose the ability to make new
connections to the Internet until I reboot...but the wireless
connection to the router is fine and any _ongoing_ links to the
Internet continue OK.

That's the crazy part -- I can be downloading streaming audio,
for example, and it will continue indefinitely, but I cannot
newly access websites with the browser or connect to the mail
servers or anything else. If I stop the streaming audio, I
can't reconnect. I've lost the ability to negotiate new
connections with the Internet until I reboot. I can access the
router menu OK, just not the Internet.

Any thoughts on this? I seem to have read complaints about this
behavior with this card, but I am not sure it's the same
problem. I have updated the drivers without any improvement.

As always, thanks for any help!