ATI HD 4890 problem........

Hi,

Unfortunately I'm still having problems with my new graphic card...

Here's the problem this time:

There's a old FPS game I play (DirectX9) and with my old graphic card (ATI Radeon X1050), I used to play with around 90~94 fps (the game's max). Now I bought a Powercolor HD 4890 and when I try to play, I get 26~30 fps...
I have downloaded and installed the drivers (http://game.amd.com/us-en/drivers_catalyst.aspx?p=xp/radeonx-xp ~ Option #1). I have updated DX9, etc...

I tried to low down all the game settings, I tried to put the graphic card at extreme performance mode (decreasing every quality setting) but the fps won't go up... I have reinstalled both graphic card's drivers and the game and no changes...

Usually in the "good graphic card with bad performance" cases, the CPU is the bottleneck. But I don't think my CPU is the problem... I have a Intel Core 2 Duo E6550. I've checked if there are any driver updates for it and there are, but the updates are for windows Vista and I got XP...

And even if one of my other components is a bottleneck for the graphic card's performance, how come it doesn't have at least a better performance than my old one, in a old game?

Additional Information:
- Windows XP: With every update.
- Motherboard: ASUS P5GC-MX.
- CPU: Intel Core 2 Duo E6550.

Thank you so much for your help so far, hope you can help me out with this one, too...

Greetz

I don't think that's my case because my cpu is good enough to handle the graphic card...

Anyone else has any other idea...?