Windows XP, ME, 2000, NT, 98, 95

Because programs are authored in a 'low level' language (= easy for the computer to understand) they will run happily on almost all Windows set-ups... 486s upwards / 8 Mb of RAM (!!!). 

Many actually run on 3.1...

Unlikely! - our programs are loaded onto hard disk - this means that there are (very) rarely problems when running them across a network.