i want to install my windows on my mac so i can use .exe and .doc files. I have found a Windows XP disc but it was already used by my dad. If i use the disc will it still work? and will it mess up the original computer that used the disc?
1. Using the same "CD" will not mess up the original installation or any other. You can use it an unlimited amount of times.
2. Its more a case of the single License key - but even reusing that across several machines hasn't caused any issues in my experience so far.
So essentially no - even so you really should buy a new license.