How does XBOX LIVE gamertags work with ROCK BAND 360?

I just got an XBOX 360. I also got ROCK BAND. I have never used XBOX LIVE at all. I know enough about XBOX 360 that i have multiple LOGONS for storage of saved games, etc (profiles). If I sign up for XBOX LIVE, would that be specifically and permanently BOUND to that local xbox name that is logged in, or does the LIVE GAMERTAG store seperate from the local?

Also, what is the IMPORT GAMERTAG option I have seen in some of the meus? How would that work (assuming I have XBOX LIVE SUBSCRIPTION?)

The girl I am staying with is way more into ROCK BAND than I am but I really enjoy having my own local profile (since I play most other games anyway) plus it gives me my own achievements, but if she gets used to logging into my profile (to play LIVE or download content etc) then she is surely to somehow "lose" a character or something, its inevitable lol.

OR, does content downloaded from any LIVE profile become available to any ROCK BAND player on the local box?

Thanks!

How does XBOX LIVE gamertags work with ROCK BAND 360?

ur name will be the same except when ull register a name that is already used by somebody else u have to change it...... BTw if u already aregistered ur name online then u can only change it by buying microsoft points........u have to pay to change ur online name....

i think import gamertag lets u save it somewhere else like Mcard LOL dunno.........

yes downloadable content is shared by users....