From the main 
web page, the minimum system requerements are:  
  
Windows 95/98/ME/2K 
DirectX 7.0a 
DX 7 compatible video card 
PII 333 or better 
Sound card and speakers 
Internet connection 
In my opinion, this looks like it hasn't been updated for the last upgrade.  I think you need DX 8.  It is free to download, so I would suggest loading it and see how it runs off line.  
From my experience, I had a AMD K2 450, 256M RAM with a GeForce 2mx video card, Soundblaster Live sound card and it was getting hard to play at 1024X768, 32bit color.  The resolution can be set back so it has a playable frame rate.  I upgraded to a AMD 1.1G (all other components the same) and I have no problems getting high frame rates.
Gunner <CAF>
[ 12-23-2001: Message edited by: GunnerCAF ]