Three cool tips from the gang at CNET on speeding up your computer. Yes, computers feel fast when they're new, but over time they get kludged up and tired.
All three of these tips are valid, and there's no voodoo there or stuff that can harm your system.
I'd add a fourth tip - update drivers, especially graphics card driver, and especially if you are a gamer. AMD and Nvidia send a lot of time optimizing drivers for games, and there can be a huge performance difference between minor updates.