8800gt to 4890, 19in to 23 in monito

I am thinking of upgrading my current system.
I currently have a Q6600 with 4gigs of ram running Vista 32 bit and a 500 watt psu. I am using an 8800gt 512 mb on 19 in monitor at a res of 1280 x 1024.

I am thinking of upgrading to a larger 23 in monitor with a res of 1920 x 1080 and upgrading my graphics card to an 4890 1 gig.

My questions are: Will my current system and psu be adequate? How much of a performance gain will I receive?

I play mostly FPS type games and I like to turn on as much graphics quality as possible.

I really don't want to have to upgrade any other parts of my system except possibly (but highly unlikely) the psu. Mem is at max and I would buy a whole new system before I would upgrade too much. I thought about upgrading to Vista 64 bit, but Windows 7 is so close now.

Hoping I can get some more life out of my system without having to drop a load of cash for a whole new rig.

Thanks!

you really should think about downloading the 64bit windows 7 for dual boot, as the addressing the extra ram will help at times. Its kind of hard to answer your question on what kind of gains you will see since I didnt' see the card you are replacing mentioned. I doubt you will see any gains in fps, since the huge jump in resolution will eliminate any gains you have in that area....in fact they might decrease depending on what card you currently use.