As I mention quite often here on HN, I'm an information security professional. I'm not talking out of my ass, I'm talking from direct, first-hand experience. No one is saying you should buy a new computer, you can upgrade an OS on the same hardware. Use Windows 7, use Ubuntu, use Unix if you want to. Just please don't use Windows XP.

For my own sanity, I'm just going to assume you're 13 years old.