the greatest hits version for ps2 has the extra scenario that was orginally only featured in the x-box version. the regular ps2 version doesn't have it. so if you want that little extra get the greatest hits version. just fyi.
If you have a Fry's near you, go check it out and see if they still have the PC version in stock... I think I got mine for $9.99. It comes with the extra scenario just like the Xbox / PS2 Greatest Hits version.