Sharing program installs amongst Windows XP and Vista

[Gordie]

Hey, I have a 160GB (rated, actually 140GB) hdd inside my laptop and I am running Vista (came pre-installed) and after messing around with XP, Vista, OSX86, Ubuntu, etc. I have decided to settle with Vista, XP, and Ubuntu. However, my main issue is that Triple booting requires lot of space both for OS files, application files, and whatever else one needs on their computer.

I am wondering if it is possible, in an effort to save space, to "share" application installations between both vista and XP. This might sound dumb at first, but when you run the Adobe Creative Suite 3 Master Collection (for work) what takes up 9GB+, and Sibelius 5 (plus high-quality sound bites) at 4GB you can see how installing it twice would eat up the HDD pretty fast. I realize that in order for the applications to be recognized in each install some registry values would need to be ammended, but I am not super familiar with regedit (like what values to export from vista then import into XP / vice versa).

Is there a program that tracks the registry values changed during the installation so I can just export the changes? Is this how I would go about this? Also, would it be better to create a separate partition to installed the shared programs to?

Thanks in advance,

Gord