These are the recommended specs for TF2:
Recommended: Pentium 4 processor (3.0GHz, or better), 1GB RAM, DirectX® 9 level Graphics Card, Windows® Vista/XP/2000, Mouse, Keyboard, Internet Connection.
You cover everything aside from the Processor power, because your total Processing power is 2.89 GHz, and even though that TF2 supports Multicore processors, 2.89 GHz simply isn't enough to handle everything that's going on, including all the Particle Effects and Physics, coupled with your quite low graphics card. All I can suggest again is turning everything down graphics wise, including your DirectX level (Just google TF2 DirectX 8 and you'll see some helpful links) Or just getting a new computer altogether.