Office 2003 Pro downgrade to Office XP Pro

[PMartineau]

We are small college, need to use Office XP pro, however
we cannot license it now, so we were told to get Office
2003 and then we could "downgrade" to XP pro.
I have the disk (office 2003) and our licenses, but HOW
do I install office XP pro, it everything I see refers to
Office 2003 only....
We have licenses for both Office 2003 suites AND Office
XP suites.
Thanks for your assitance