I've managed to contract a couple of viruses over the course of PC ownership, but unless it's a really new virus, there is usually a fix for it. Either from Microsoft with a patch, or a even a file that will heal your pc from the likes of Nortons. Virus antidotes are often free for download from places like Nortons and McAfee. The first thing I always did was find out what the virus was, what it's name was, and search for an answer on Google. You'll not be the first person to get it, and there will no doubt be a huge knowledge base out there just waiting with an answer for how to get rid of it. If you can't find the name, describe the symptoms into google. Formatting the hard drive is so final..
I use and recommend
http://www.avast.com/ . I've tried Nortons and McAfee and AVG. This one is light on the system, and picks up things even after McAfee thinks I'm clean. Maybe then your brother won't mind keeping it on. Oh yeah, it's also free.
Edit:
For example: Avast have a virus cleaning tool on their website. Free to download and gets rid of most of the major nasties to hit Windows.
http://www.avast.com/eng/avast-virus-cleaner.html