Upgrading to Parallels 5 and Win-XP license

Hello,

About a year ago I upgraded from Parallels 3 to 4, and as part of the installation I was required to enter a license number for Win-XP. It wouldn't accept the old license, and I had to get a new one - a big hassle! I'm interested in upgrading to Parallels 5, but wish to keep my existing copy of Win-XP. Is that possible, or will the upgrade require me to buy yet another Win-XP license?

Currently Paralells 4.0.3848 running on Macbook Pro with OSX 10.5.8 (Leopard) but might soon upgrade to Snow Leopard.

Richard