installing two versions of same program

i'm doing this little project on a pc that isn't mine. i installed the software i needed. the pc breaks. i do mean breaks, not crashes.

they got a new pc. it came with a newer version of the software i need. the newer version doesn't have the features i need, but does have other features i need because the new one lacks other software that was on the old (based upon hardware issues).
this is where the question arrives...



is there a way for me to install the old version in a way that keeps the new version?
simple answers like 'changing the destination folder' do not need posted.

I'd try something like this http://portableapps.com/

Then if that doesn't work, you'll probably end up doing what Toast said. I'd recommend VMWare or Microsoft Virtual PC.