Guitar Hero question.

Ok so, I was told the following :

If you are gonna buy Guitar Hero III for any of the 4 consoles you need the specific guitar.
So then I must buy the PS2 Guitar for my PS2.

But can I play GH I and GH II with the GH III Wire Guitar?
I was told I can't but that doesn't really make sense to me.

Thanks in advance.

Well, the GH2 controler works for GH3 so I think you can play GH2 with the GH3, but for 1 you need a GH1 controler. Also, he GH3 controler works for rock band in case your interested.