If your OS is XP or higher but not vista, then Mircosoft with send you a patch code, it the program is legal. Be warned it you run an illegal program Mircosoft will pick it up and send codes to disable you OS. Then your hard disc will crash.
If its correct with the right key codes you will not have a problem. But trying anything before 2000 is iffy because MS no longer provides support for that and many virus and worms attach to lower out modded systems and programs.
Run an AV through it first before installing anything on the drive.
How do you determine whether or not the software is legal?
First of all I am guessing you have an illegal copy. What you are looking for is the Official Microsoft icon on the disc the box and any paper work you have with it. Legal copies are what is brought from a store.
Burnt from another disc, downloaded from someone Else's computer, or even brought from a computer swap meet are
illegal copies and breach of copy right to Microsoft.
They generally only come with a code program not the correct code. And Company copies are also not legal due to you are not the licenced holder.
If you have downloaded it off the net via the Microsoft site you are fine.
There are freeware programs available off the net google freeware you will find a program to suit.