I'm sorry that you are having issues with your PC. Get NIS 2010 and forget your worries. If you feel that you are more secure using a Mac, think again. As Macs sell more, there will be more hacks/exploits developed for the Mac which will expose it to the same security risks as you would see now on a PC. Remember a hacker will develop hacks to gain the most $$$ on as many systems as quickly as possible. I guess it also depends on what you want to do with your computer. If you are going to do itunes, surf the web, and check email, then a Mac will probably fine for you. If you are into gaming and other applications, the PC has vastly more available for it.

One recommendation I would make is to use FireFox and use several add-ons such as No Script and AdBlock Plus. This provides a much safer surfing experience.

apple free zone for... well... since forever.