No, Guitar Hero 3 has no DLC, if you wanted to put new songs on it you'd have to hack it somehow. The new Guitar Hero: World Tour will have DLC though, you'll be able to download songs onto and play songs from your SD cards (they will probably let you download all the songs from the previous games). If you want more info on Guitar Hero: World Tour for Wii check out the Related Linksbelow.
you can download songs online and insert it to your guitar hero game. search how to download songs to guitar hero two.
You can't download songs.
no.. not at this time
No
you cant
No
nope
In the shop on the main menu. There is an option there to download the packs, for a price or for free if you have an owner's code, which will be on the book in the game you want to download the tracks for.
You can't.
Illegally, yes
Most of them, but not all. There are Downloadable songs which can be downloaded for free, but data charges may still apply.
No. How do you expect Guitar Hero to make any money off of download-able songs if people can just play their own?