No that is not possible...windows XP, because of the validity checking is designed for a single computer's harware configuration. Changing the hardware will cause a failed fault check and the operating system will not start. Besides that it is against the EULA agreement that the operating system must remain with the original computer it was installed on.

************************************************** ***

You can use that reformatted drive on the Vista computer and install XP on it then the office 2000 program as in a dual boot configuration.....I personally would use a third party boot manager such as GAG or BootIt NG (google is your friend) as it makes the installation much easier.

************************************************** *****

Is it that office 2000 just will not install or will not run once it was installed...
Windows Vista has a compatability program that allows th running of installed programs in a virtual setting of the desired OS.....

1)Right click the executable and click the Properties option.
2)Select the Compatibility tab.
3)Select the Run This Program in Compatibility Mode option.
4)From the drop-down list, choose the operating system you ran before upgrading to Vista.
5)If necessary, select the option to run the program as an administration.
Click OK.

If there is a problem with a driver file not running in Vista then it won't work...but worth a try