Why is our Internet connection dropping off?

We have a 3Com Wireless and Wired router and we have 2 computers connected via wire (cat5e) and my Wii connected to the wireless. But our internet connection only drops off when you use a web browser on a website with a lot of graphics (I.E. Yahoo, Google Images, Myspace, Myyearbook, and Youtube) for a short period of like 3 minutes or so and even sometimes randomly ... but if I let it sit on the website for a minute or two and not clicking anything and then click something it loads most stuff ok but it still drops my connection after a bit anyways (it slowly stops loading flash ads and banners and then images and then whole pages) .... and it is kind of slow now even though were only running at 512kps ... I have reproduced this issue with my machine running Windows Xp Pro and Ubuntu 8.04, my parents machine running Xp Home, and my Wii, I have tried several web browsers as well .... I have argued with my ISP about this for about 4 weeks now and I have gotten no where with them (they send our internet via radio signal to a tower on our house that goes to a breeze unit and that goes to our router) ....Our Isp keeps telling me I have a boot sector virus .. but how is that possible if my Wii can reproduce the issues .... I unplugged my parents machine From the network and I have set my machine to run raid 0 with Xp Pro after a reinstall and and deleting Ubuntu and it still can repeat the issue ... ive checked host tables and running processes on both computers in xp and turned up nothing ... I think our hardware for the wireless radio connection is jacked-up ... but my ISP still says its a virus on our network or our pcs ... anybody help?
P.S. If you need more information please ask ...