You can re-register at any time, and you receive a key good for 14 from NOW. I.e. if you register now, you will get a key valid thru June 05. If you register in July, for example, you get a key valid thru Sep 05, etc...
If you use the same e-mail address, the "customer number" part of the key will stay the same (the 7 digit number that follows the letter at the beginning of the key).
Hope this helps,
Vlk