Help, my PC can't run any decent game

[Flow]

What'up guys?

 

Would you kindly help me out with this? Take a look at my pc:

GeForce FX 5500, 256 MB video card
Intel Pentium 4 1.60 GHZ processor
1024 ram

 

Well, i'm no real expert at this, but i think that's all that matters, right? If you need more specs i'll give it pronto

I recently bought Team Fortress 2 on Steam, and even though my pc seems to fit in the minimum requirements, the game is unplayable, even on the lowest settings

I wonder if i need to upgrade my PC or it's probably something on it's software?

Thanks in advance