Q: When I sign up for a completely new Xbox Live account can I use the profile that has all my previous achievments or will I have to make a new one or just change my name on the profile and sign up?
A: Yes you can keep your old account just sign in with the gamertag you want to be live and make sure your 360 is connected to a broadband connection and go to the xbox live page on your 360s main screen and click join online community or something like that and just fill out everything that pops up it will scan your gamertag and if someone already has it you can rename your gamertag and if you have to do this make sure its something good because changing your name costs 800 microsoft points later