Yes. I can play "guitarhero".
nope
the only way is to either play the campaign on a different difficulty, or cheat
drums
Probably.
no
It's not possible. The PlayStation 2 version does not support Downloadable Content, and never will. If you want to play DLC, get a PlayStation 3 or Xbox 360.
There are 49 songs in Guitar Hero: Metallica.
There are 5 frets on the guitars and 5 drum pads on the drums.
I don't see a big difference.
The guitar can be used as a guitar or bass.
I would love to answer your question, but please be more specific on what exactly you want Guitar Hero Aerosmith compared to.
Yes. ...And you had the rock band beatles instruments, it would also work the other way