Steady Degradation Of Network Connection

I recently upgraded from vista to Windows 7 and I have noticed that whenever I want to visit a website (this one included) i often have to click the link twice for my browser (firefox) to change pages. The first click sends the request and eventually times out. While the progress bar stalls out at about 50% if I hit the link again it goes right to the page. If I go to speakeasy.net and test my connection, 1 attempt will correctly display my 20mb connection, the next attempt shows 2mb, while further attempts either show any speeds in between or it will just time-out eventually.

My upload speed is always correctly displayed at about 2mb. All other computers on my network have no trouble. I have my network card set for 100mbFD (changed with no effect from auto negotiate. When I try and download files from the Internet (drivers, documents from attachments etc...) my transfer speed slowly and steadily degrades from 1mb/sec to idle. If a file does actually come close to fully downloading, the file ends up corrupted due to data loss, or it cancels completely due to lost connection to server.

My motherboard is asus M2N-SLI Deluxe with current nvidia nforce driver 73.1.4.0. Using the device manager, Windows 7 shows my driver to be up-to-date (which is false because it said the driver it found for the card was current, but it isn't) and nvidia's driver manager also shows my driver to be up-to-date.

Even internal network transfers suffer. Files from my file-server also start out fast and continue to deteriorate to idle.

I'm a pretty novice network person, but I've looked at my router/firewall, device manager, Windows 7 network settings and nothing seems abnormal or unusual.

Like I said, every other computer on my network has 'normal' connectivity and it is just this comp. Any ideas?