I would Get a Good quality UPS (Uninterruptable Power Supply) they are about $150US. This will stop the power supply problems and give you time to shutdown correctly or can also be setup with software to automaticly shut the computer down after a set period in the event of a power failure. They also stop voltage fluctuations (Average +50 per day) that can cause all sorts of problems with computers. Download all the windows updates which fixed problems i was having with SP2 when i first installed it from a download and keep your virus scanner up to date along with anti spyware software Eg; spyblaster, spybot & Ad-aware all free. also follow psy clops's advice. Also make sure all your drivers are up to date as well.
John