If you really want a PC where you don't have to constantly worry about security, you need to switch to desktop Linux or a Mac. It's not that they're perfectly safe either, they're not. It's just that they're safer than the Windows alternative, and that includes Windows 7.
This isn't just my two cents. I'm told by friends at security companies and Microsoft that the problems that will be patched this time around in Windows 7 are the exact same kind of problems that Windows has always had. When it comes to Windows, it really is a case of the more things change, the more they stay the same.