Trans Magic Players:
If you need to change the name on your DCI account it is actually pretty easy.
You can either email WotC http://wizards.custhelp.com/ or you can call 1-800-324-6496. I called and the person who helped me was quite pleasant and the change will be immediate. I am not sure how long it takes for the email process to take.
Additionally, if you have a DCI username (which is just for logging onto the DCI website) and you need to change it there is an extra step. You need to create a new DCI account with a new DCI number and everything. Then you use that account to make the username you want. Then contact WoTC and they will merge the accounts, allowing you to choose which username to keep.