Depending on the program:
a. It won't run at all.
b. It will run but not fully (for example, if it's a picture editing program you won't see in the list of programs when you choose Open with ... for a .jpg file).
c. It will run as it always did.
The best way is to reinstall from the original setup-program or CD.
I have lots of programs and miscellaneous stuff on an old PC and and a Maxtor external hard drive...installed in the past five years or so. I haven't bothered to look for software installation CDs yet, and I'm not sure where to look.
If I get a new PC, will I be able to copy the Maxtor structure to the new PC and have everything work as it does (or maybe even work better) on the old PC? I'm running XP now. If I can move the old programs from the old PC or the Maxtor drive and have them work as before, would it matter if I had Vista or Windows 7 on the new PC?