AGP2x/4x compatability?

I am trying to determine what new graphics card to get so I can play the neverwinter nights 2 game soon to be released (requires 128mb graphics ram, pixel shader 2, Geforce FX 5500 or later), preferably without putting in a new power supply, if possible (I only have a 250w).

What confuses me are the AGP specs: some specs I have say I have a 4x slot, some describe a 2X/4X slot. Am I able to put a 4x/8X card into a 2x/4x slot? I would guess not, but the choices for 2x/4x boards seem very limited.

Your opinions would be appreciated, thanks.

I attached my system specs.

 

Yes you can put a 4x/8x agp card into your computer it will run at 4x because that's the fastest bus speed your computer supports.

 

Oh, good. Then I have many to choose from.

Thanks.