well heres the deal its actually not guitar hero i believe i think its actually called frets on fire and even with a ps2 you can mod it and put your own songs on that because they created the program to do it and its out for public use proabably not the most legal thing in the world seeing as a you have to mod your PS2 and such but i have seen it and played it you just have to be really good at making the songs and such but once you get good there are no ends to how much fun you can have ive even seen people make some stuff for super mario and stuff such as one winged angel which is really wierd seeing as there is no guitar but meh whatever...
No. There's actually a PC version of Guitar Hero III now. o.O And you don't have to make your own songs for custom songs. You can download them, usually in a .chart format. And while, yes, there is a program called Frets on Fire, it sucks, needless to say.

And actually, there is guitar in One Winged Angel, it's just not the main instrument in the song. Note: The Black Mages are freaking awesome. (So is Nobuo Uematsu, who, in turn, is the creator of The Black Mages, and the keyboardist, I think. o.O)