Does the OpenGL section in TrainzDiag show a pass llike this?
		
		
	
	
XP is pretty much just NT in a pretty frock anyway so it probably won't make too much of a difference for the driver.  
I'm not too well acquainted with ATI cards, I've always had nVidia ones.
If you post the dxdiag details I'm sure someone more in the know with ATI cards will help us.
Here's the relevant section from my dxdiag report as an example.
---------------
Display Devices
---------------
        Card name: NVIDIA GeForce Go 7900 GS
     Manufacturer: NVIDIA
        Chip type: GeForce Go 7900 GS
         DAC type: Integrated RAMDAC
       Device Key: Enum\PCI\VEN_10DE&DEV_0298&SUBSYS_FF311179&REV_A1
   Display Memory: 512.0 MB
     Current Mode: 1600 x 1200 (32 bit) (60Hz)
          Monitor: HP LP2065 LCD Monitor
  Monitor Max Res: 1600,1200
      Driver Name: nv4_disp.dll
   Driver Version: 6.14.0011.6909 (English)
      DDI Version: 9 (or higher)
Driver Attributes: Final Retail
 Driver Date/Size: 11/11/2007 17:51:00, 5770880 bytes
Mike.