If you encounter a page that simply asks for an email address, this is because THE KEY YOU INSTALLED WITH HAS ALREADY BEEN USED.
Solution: Generate more keys untill you get a good one. You will have to put the new keys into the registry - this is a simple process:
[START] > [RUN] > type "regedit" [ENTER] > open: HKEY_LOCAL_MACHINE\SOFTWARE\TrendMicro\PC-cillin > find 'SerialNumber' [RIGHTCLICK] and 'Modify' to paste in the new key.
Start Trend Micro again and attempt to activate. If you get the screen that asks for a single email address, try another different key. If you get a screen asking for multiple details, fill them out and your done.