Disconnecting every so often, any ideas?

Hey,

I've now hooked my computer up via wireless, have been using wired for years previous.

I'm using http://www.tp-link.com/products/product_des.asp?id=47

I'm with Sky Broadband, with a Sky branded Sagem F@ST 2504 router. I have two other laptops connected, which don't have any problems, even having a laptop downstairs - it'll run fine, my computer is the only problem. I'm two rooms away from the router, and my signal is always Great-Excellent, so it's not like anything is in the way (it's a brand new house, so obviously the walls are pretty thin)

When it disconnects, the "limited connection" thing that Windows has comes up, and then the red X will appear over the network icon in the taskbar, and then reconnects a few minutes later, when it reconnects, it asks me for my router username and password for some reason (the admin/admin thing)

It's not a problem with channels, I've tried Auto, 1 and 6 - and it just does the same, and it's set to 54g Performance (other choices are 54g auto and 54b only)

Any ideas what it could be?

If you need them, here's my specs:

Windows 7 RC 7100 (it did the same thing when I had XP)
AMD Athlon 64 X2 6000+
4GB PC2-6400 RAM
nVidia 8600GT

Thanks guys!