for whats its worth, windows XP got rid of a lot of the problems and crashing issues... im not saying its perfect, cause yes, it CAN crash... i think i crashed xp once... and that was with an already corrupted install.
i accomplished it by going into the system folder and randomly deleting things that sounded important.
i trimmed down about 30 megs of stuff before windows got flaky, then i got about another 10mb deleted and boom, she went down.
repair installs allow you to fix MOST things that go wrong without reinstalling all the apps.
about the licensing thing... its only an issue if your using a cracked cd, a warezd copy, or if you reinstall on a monthly basis.
even if your using a "non-registered copy" for whatever reason, theres ways and means around it, if you choose to break the law.
most people do a critical upgrade about once a year, maybe not nearly that often, and with XP, ive found thats the ONLY time you need to do a full reinstall, unless you get a virus and are unable to remove it properly.
just my 2 cents on windows XP...