Rather than have two physical computers just run one.
Have a Windows Desktop(if you prefer), and run a Linux(or Windows) Virtual Machine to go online with. If you need to download/save anything from your online session, use removable media, or network storage of some kind. When you’re done with it, just revert the VM to snapshot(a pristine copy of the VM). Since you saved any data to removable media/network, you won’t lose anything when you go back to the snapshot.
That’s a pretty solid setup. I doubt it would help anyone with the exploit written about on this thread though.
I like your idea. However, the friends I'm advising would not understand a word of it. ;)
In this age, computers are so inexpensive, especially if the only software you're running is for internet access and anti-virus apps, that most of my non-technical friends are able to accept and understand what is required. If this box gets corrupted, a wipe and re-install is simple, even for most of them.