Before doing the restore, download a trial of Webroot's SpySweeper. It will likely get rid of that for you.
On my PC, I use a combination of several things to keep it virus and spyware free - and none of them are too expensive or difficult to maintain.
First, I have the router which serves as a firewall of sorts by assigning IP addresses with DHCP. You can set up MAC filtering and all sorts of other things, but I haven't and have not been hacked.
I also run Norton Internet Security and Webroot SpySweeper. I also have the Windows firewall on. Keep everything updated and run the auto-scans and your dad can be about as safe as could be expected on a PC.
Oh, and tell him to stay outta the pr0n - LOL! Seriously, there is no substitute for common sense when surfing. Avoid sites for hacks, key gens, free ringtones, and stuff like that. If you get a pop-up - and I rarely do - do not click on it anywhere except to close the window.
You could be a good son and tell him to get a Mac, but of course you already did that.
Change his homepage to Apple.com where they are running the new ads.