dwright said:...Ideally i don't want to have to delete cookies each time I use the computer...
So cookies are the problem? If so, you can:
1. have cookies automatically removed upon closing the browser
2. use different browsers (eg you use IE and your dad uses FF)
3. set separate (optionally password-protected) profiles with FF
4. use separate logins for Windows so IE will not use the same cache/cookies (similar to #3 except with ugly 'ol IE)
I read through everything above, but...what is this about installing additional software (duplicates), OS's, etc? That's crazy... but I am curious, just what software are you going to try and install twice? Internet Explorer? (No pun intended, of course!)
Edit
Ack, obviously I didn't read throughly enough...this is a program you download and not a website itself?
/Edit