Sure.
First things first. Windows XP and 256MB of system RAM is not healthy, I would advise you at least double the RAM level, to avoid games like RCT having to make excessive use of a paging file.
Now thats out the way...
Analysis of the DxDiag reveals that you have an AGP slot, so your choices are limited. Something like an ATI Radeon X1600XT should do the trick in your system. It's not to expensive neither, coming in at just over £130 over here in the UK. You can also choose to have a X1600 Pro, which is slightly slower, for just over £100.
Nvidia also have some decent offerings too, altho, slightly more expensive. You can get a GeForce 6800GS for £165, or the much faster GeForce 7800GS for £215, and that is the fastest you will get for AGP.
Any of those will work fine. As a general rule of thumb, don't buy any card below around £100. They generally are not that good. Also, dont pay extra for cards with 512MB of on board memory. All of the cards I mentioned are no where near powerfull enough to process graphics on resolutions high enough, and detailed enough to fill that memory. Stick with 256MB, it will save you a few £££.
There are also some to avoid. Purchasing any of these graphics cards is a waste, as they are dated, and many lack DX9 certification:
- Nvidia GeForce 6200 Series
- Nvidia GeForce MX4000
- ALL Nvidia FX Series Cards (5200, 5600, 5700, 5800, 5900, 5950)
- ALL Nvidia GeForce 2/3/4 Series Cards
- ATI Radeon X1300
- ALL ATI Radeon 70xx Series, 80xx Series, 9200 and 9250
- Anything made by S3 or Matrox
Yeah, thats it... I can't believe that some online retailers are still selling some of the older cards too. Still, I hope this has helped in some way.