Include in the body of the email the following information:
->the account name ->the character name (if applicable) ->a DxDiag (see below) ->as much information about what you encountered as you can, including error messages or screenshots
NEVER send us: ->your password ->your full credit card information
A DxDiag is a utility designed to display the specifications of the user's hardware, as well as to test DirectX software, including sound and video. If you are asked for this information in an email, it helps the support group relate your gaming issue to your personal computer.
To create a dxdiag.txt just go to Start -> Run (or Search in Vista) and enter dxdiag and click OK. Once the program has run its course, click "Save all Information" and it will output a txt file that you can attach to your email.
The more information you give up front, the faster your issue can be resolved.