Flaky performance on xp, ok on vista

Hi,

There is an issue on my wireless setup and unfortunately I'm not being
able to figure out the way to fix it.

I'm using an Acer Aspire 5050 laptop with an Atheros AR5005G wireless
adaptor.

It came with Windows Vista and the network works fine on it.
Now I have installed Windows XP SP2 and I can run both OS (dual boot)
on the same laptop.

The problem is, on XP, from time to time, the network performance
falls dramatically: web loading is extremely slow and incomplete, or I
don't get any response at all. Not only web, but every internet
services stop working. The router configuration web interface fails to
load properly, too. Pings to the router get very long response times
(hundreds of ms) or no response at all. After some frustrating
minutes, the issue is magically fixed and everything works fine again.

It only happens on Windows XP, never on Vista (on the same laptop).
The Atheros AR5005G driver for XP is the latest from Acer support site
(ver. 5.1.1.9).

I think the issue is exactly the same as described here:
http://www.futurehardware.in/569604.htm

Any suggestions?
Thanks in advance.