Lost connection

In June of this year, I switched from dial-up connection
to high speed wireless connection on my internet. In Aug,
I started having trouble keeping a connection. I would
have to "Disable" the network card and then "enable" it
for it to work. I also can't do a windows update, it
won't stay connected long enough. I've tried a new
network card and it did'nt help. I moved the computer to
another ISP with DSL and it works just fine, even get a
windows update. My ISP says their are other people with
the same problem with Windows XP, but it's not true. I
don't know what to do next. Does anybody have any ideas?

Thanks!