A very simple way. Go buy a Mac, or, if you don't have the money or it isn't time to upgrade yet then just use Ubuntu instead of Windows, that won't require any new hardware.
Their is no way to NEVER have spyware until M$ releases an OS that is more linux like. The registry and DLL's and every way Windows operates makes it a natural haven for adware and viruses and etc. So as long as you have Windows, no way to stop them, I mean, you can try and do a good job, but it is a lot of extra time to protect yourself, when you could be doing something else, plus you have to upgrade AGAIN, to run all these anti-adware programs.
In the meantime, OS X Leopard can run on 6 year old systems just fine and Ubuntu can run fine on a Pentium 2.... plus they are both highly secure.
Ubuntu is completely free and all the software for it is free and it can run windows programs. Mac's start at $499 for a mini and $900 for n iMac, so they aren't as expensive as people say.