Internet browsing/Uplink issue

Hey guys, I've been having this annoying problem for afew days now, and really want some help fixing it.

It started with tuesday I think, when my friend was downloading a big file from me via my FTP-server. He is always able to download stuff at 1.2MByte/s from me, as that is my Fibre uplink top up speed (10Mbits). Now, he was downloading at that speed, until it suddenly dropped below 10KB/s. It stayed around that, and then got up to 1200KB/s again. Then, it repeated more and more often, sometimes he got disconnected completely. All this time, I was talking over MSN messenger with him, and that worked fine.

Then, my browsing got sluggish. I could wait forever for pages to load, until they loaded, and I could click several links and eerything worked fine as usual, and then I'd have to wait for pages to load again. It got me a looong time to get to this forum, registering, and start to write. I can barely browse the internet at all, and It's really annoying.

All this time, my torrents are coming fine at normal speeds, 100-600KB/s. I am still able to talk via MSN Messenger and Skype without any problems. When I close utorrent down, internet browsing is still slow.

I've tried restarting my router (Dlink Dir 301), resetting the router, did a boot scan for viruses using Avast.

I am using Windows XP SP2, I am not connected wirelessly.

Please help.
/Skepparn