Build and Shoot

I love Ace of Spades... or Build and Shoot but this game is so laggy!
I max out around 12 FPS. Why?? My PC is decent. I can not find an answer to fix this issue. Can someone PLEASE help me on how to increase my FPS?
Specs:
ATI HD 5850
Intel Core 2 Extreme CPU Q9300 @ 2.54 GHZ
16 GB Ram
64-bit
This is way more than enough to run this game perfectly.

Pretty sure there's 3+ more threads like this, you can probably find your answer there.