I totally empathize with you. I have my own approach and I'll happily share it. Some might think it's overkill but I have found it serves me very well.
These days I keep my PC ultra-clean. Windows 7, Firefox, Office, Visual Studio, and a handful of freeware I have come to trust over time. I don't do PC gaming so that's about it.
For anything and everything else, I use Virtual Machines. If this is new to you check these out:
I have three VMs set up running Linux Mint 17, Windows XP, and Windows 7. I can have them all running at the same time (very cool). By setting them to use bridged networking they appear on my LAN as independent machines alongside the host PC. And of course they all have internet access through the host PC's network connection.
Now for the fun part. VMs are isolated from your host PC. You can trash a VM and there is zero effect on your host PC.
While a VM is running you can take a snapshot. Then you can do terrible things within the VM like install nasty evil software, fiddle with the registry, delete system files, whatever you want. At your will you can revert to snapshot and your VM is instantly back to exactly how it was.
But perhaps most importantly, you can do real meaningful work in a VM just like on a real PC.
One thing you need to be aware of is OS/application licensing. Running a VM on your PC means you effectively have two PCs (host PC + the VM PC). I had to purchase a separate copy of Windows 7 to install on the VM. Linux Mint? Well it's free and open source so you can do what you like with that ;-)
EDIT: SECURITY CONCERNS
VMs are exceptionally well isolated from the host but they do still execute on the host. Malicious software could be designed to find a way to escape the VM and do things to the host:
However, so far as I know, no such malicious software has been seen in the wild yet. That's probably because the folks creating malicious software don't see VMs as a big enough target. I mean, most people don't run VMs let alone know what a VM is.
Perhaps more importantly then, if you enable bridged networking on a VM like I do, it becomes part of your real LAN. That means malicious software running in a VM could attempt attacks on other devices on your LAN or other machines on the internet.
So even with VMs it pays to be careful. Keep everything up-to-date and use anti-malware software on your host PC and in each VM. Putting aside academic possibilities, 99.99% of the time when your VM gets trashed by malware your host will be totally unaffected and revert to snapshot will get you out unscathed.