Vista Business Trial Ended Now Im Stuckhttp

I got a new hard drive and decided to install vista to see if i liked it. Now my hard drive i use normally with winxp crashed and I figured I try the Vista Hard drive. Anyway the Vista I installed was a trial and i have no key. I'm happy with XP and would like to downgrade to XP. I cannot do so because I cant log into my desktop it ask's for my windows key. then brings me back to the login screen. I tryed to get to the Boot Menu when i restart and it wont work. I dont have a F lock on my keyboard, and I cant seem at all to get the XP CD to run. Thanks in advanced for anyone that can help.

Also if you can help with my Hard drive that wont boot heres the link to my post and I thank you again!!
www.tomshardware.com/forum/253018- [...] boot-winxp

-Andrew

Just for your information, there is no such thing as a trial version of Windows.
If you didn't buy it, you had no legal right to install it.
The 30 days allowed to activate the program is a grace period given to you so that you have time set it up and to contact Microsoft for activation.
For instance you buy a new computer, you don't have an internet connection, you need time to select an isp and get connected to the internet before you can go online to update your security and get your legal copy of Windows activated.