If there is a general election before December, it will be conducted on the electoral roll drawn up on the basis of October 2006 data. If you have moved in the last twelve months, you will need to re-register (a form is available from the ERO in Port Talbot civic centre) at least 11 days before any election. To reduce a last-minute log-jam of applications, people wishing to vote should re-register as soon as possible. It would be as well not to wait for Gordon Brown's announcement.
If you are away from home (for instance, in college), you have the option of registering here or voting back home. If the latter, make sure you know where your polling station is located, if you want to vote in person; otherwise, apply for a postal vote in good time.