I think the decision depends a lot on whether you have a decent computer and/or are willing to play games on it. I say this because many of Xbox's games and many of its "exclusives," like KOTOR, Halo, Splinter Cell, Doom 3, GTA, Counterstrike, are or will soon be on PC. Even if you have a crappy graphics card it could be be 1/2 the price of a new console. IMO some games are better played on the PC because of the precision of mouse control and the keyboard. Also you may want to consider how important graphics are to you, because Xbox multiplatform games typically look better than PS2's, and how much you like FPS/Sports games (the main Xbox game genres).
Edit: Few more things--
-To play DVD's on Xbox you have to buy a $30 dollar remote.
-PS2's often need to be repaired. I know 6 or 7 people who have broken or semi-broken PS2's.
-For Xbox live you need to pay $50 a year (I think, not positive about amount), and PS2's service is generally free unless the game requires a fee. And you need broadband.
-On the PS2, for more than 2-person multiplayer you need to buy a special multitap.
-See which controller you like better, it is VERY important.
But of course the most important thing to consider are the games, and especially exclusive ones. For me, I can get almost all of the games I want on my cube or PC.