I'm having similar problems but for me I can play on my 360 seamlessly but when it comes to a bit of TF2 on my laptop It lags loads (even on lowest graphics) and makes it unplayable most of the time.
[http://www.speedtest.net]
my laptop has:
2.0Ghz AMD Turion64 X2 processor
4Gb of RAM
NVIDIA GeForce 9300M G 256 MB
and I am running windows 7 32bit.
Also some one else posted a link to a gamebooster program and avast thought it was a virus so I didn't get it but if anyone knows for a fact that it isn't a virus please let me know!