In order for the trial subscription to become a full subscription you will need to purchase a full copy of Windows 7 (sorry kinda hard to understand what you mean).
Are you running this from within Virtual PC? XP Mode typically doesn't have a time limit associated with it unless you are using a non-genuine version of Windows 7 Pro or above which all include XP Mode natively.
Just in case you were getting ready to ask (or already did in some way) about us giving you a product key:
It is against Tom's Hardware policy for any active forum member to assist with anything in regards to illegal activities such as piracy, cheating, etc.
Please refer to
this thread for further assistance.