This is not easy to achieve. For simple apps, such as FireFox, you can simply invoke it from the shared drive inside the vm.
However, for complex apps such as Microsoft Office, that won't work. The reason is Microsft Office has lots of registry settings. In order to make it to work from vm, you will have to import all registry settings for Microsoft Office.
I can think of this way, find all registry settings installed from Microsoft Office, dump out to a .reg file, then edit the .reg file and change all paths in the .reg file to point to the mapped shared folders (c:\progam files\office --> z:\program files\office, e.g.). Then you import the .reg file to your xp vm. This will make Microsoft Office to work.
As you can see, this is a rather difficult task, and requires quite some expertise.