It actually runs a bit better on PS2, some special effects look better (probably PS2 Specific filters or something) animation is a little faster (not much but you'll feel a touch sluggish swinging your sword on PC).
If you dont have the higest end PC you;ll probably have to lower a graphic setting for the best frame rate you can get, where as there is no setting on the PS2 and it runs as good as it can.
Honestly aside from that, your play experience wont be any different between the two. The interfaces are EXACTLY the same but the PC controllers out there arent anywhere near on par with a dual shock 2(I strongly suggest if its a choice between keyboard and controller, pick controller).
My experience comes from being a part of the PS2 beta and buying the PC version afterwards. When I get my HDD I'm pretty sure I'll be playing more on that than my computer, but if you can run it on you PC and it's a cheaper option for you you wont be dissapointed even on lower graphic settings.
(but you might want to turn off the animated character selection on PC.)