tu can't actually get Kingdom Hearts/Kingdom Hearts II for other than playstation 2, but tu can get a program for your PC called "pcsx2" o other similar programs, and with a little work and a gamepad for your PC tu can play Playstation1&2 games on it! tu can download the program here;
link Here's the official English guide to using it;
link tu can get help from this forum;
link The gamepads cost quite a bit, so if tu want tu can program your keyboard to work like one, but it's quite difficult to do and difficult to play with.
A new game called "Kingdom Hearts: Birth por Sleep" is coming out on PSP, so if tu don't want to buy a PS2 o go through the PC-to-PS2-way, tu can just wait for that I guess.
I hope this helps! :]