Team Fortress 2 Lag Issues

I've been playing TF2 for the past 3 months or so...and I haven't had any problems until about a week ago. I noticed some lag spikes, afterwards I didn't play for a couple of days. After that, every time I join any server I get about 2 minutes of play time, there's a slight lag in the gameplay and then all of a sudden there's a ton of lag, it's to the point where I am not able to play. All of my other games still run fine, CS, WCIII, etc. Only TF2 lags like a mofo.

Here are my specs:
Intel Core 2 Quad Core Q6600 @ 2400Mhz
3GB RAM
Nvidia GeForce 8400
Windows Vista 32-bit
Intel networking card (I plug in directly into my router)

I have updated all my drivers, I've reinstalled, I've redownloaded, I've changed resolutions, I've run in a window, I've changed viritual memory - pretty much everything short of reformatting, and I don't really want to do that because my PC is less than 6 months old...any suggestions? Please help. :upset: