Acceptable frame rates, image quality, and game experience are personal preferences and vary from person to person. I say that because of what I'm preparing to say.
While you will definitely need a better graphics card for DOOM 3, you may also want to consider a faster processor (say around a 2.6 Ghz P4) and add about 512mb more RAM to your system (if your motherboard supports these upgrades). What you have now is (I think) above the game's minimum reqs. (except for that 5200), but these days those are pretty much wishful thinking for a high end FPS.
If money is no object, get an ATI Radeon X800 or an nVidia Geforce 6800 (if your power supply is rated at 480w or better for the nVidia). If money is a concern (like for most of us), you might want to look at the ATI 9800 XT or the Geforce FX 5900. You might be able to "get away with" a Radeon 9600 XT or a 9800 Pro, or
possibly a Geforce 5700, but I think that would be pushing it. And as I'm sure you know, no card is ever really future proof, and a game like DOOM 3 will probably stress just about any card out there right now.
And
http://www.pricewatch.com/ is your friend :wink:
