Is Windows Vista prone to constant 'Not Responding' messages, or is my computer's processor just too slow?

Without fail, my computer is guaranteed to display a 'Not Responding' message whenever I use it. This is the first computer I've ever owned and I bought it a year ago from Dell; an Inspiron 530 dual core. I had a problem with registry corruption and had to re-install windows, so I've been EXTRA vigilant about defragging the registry DAILY. Yet, someway, somehow, I always end up waiting for my computer to get out of it's OWN way, so to speak. (Windows is not responding; Windows Media Player is not responding; Realplayer Downloader is not responding; Internet Explorer is not responding; Google Chrome is not responding.) Just give me an "All circuits are busy, please try again later" and be done with it!