This idea came to my mind circa June 2005, and I don't know whether other people already use this trick.
Software companies typically release demo or trial versions of their programs that work for a limited number of days and then either stop working, or disable many features - requiring the user to purchase the software in order to access its full functionality.
If one could quickly reinstall Windows somehow (a fresh install), one would be able to repeatedly install the trial software and use it in trial mode (in which it provides full functionality).
Create a c: partition that is less than 4475 MB, and install Windows on it. Next install other useful programs that you use. Now install the trial programs that you want to use infinitely. Finally, make a 'disk image' of c: partition on a DVD, using a program such as Symantec's Norton Ghost. Every 30 days (assuming each of the trial programs expires after 30 days), simply restore back the c: partition from the DVD - the trial programs shall never realise that they are being used over and over again.
Remember to never keep any user data on c: else it will be wiped out during the restore operation. The restore operation should take less than 30 minutes, and 30 minutes every 30 days is definitely worth this benefit.
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