Get a good anti-virus program, and try to use it to remove the virus. I really like F-Prot Anti-Virus because it has worked very well for me and my clients (there are many choices):
F-Prot Anti-Virus (free for 30 days; by FRISK Software, in Iceland)
One more reason to like F-Prot -- they're anti-spam, and they confronted the Anti-Virus industry on it
(F-Prot has a free 30 day evaluation period, and then after that it's $29 for up to 5 computers at your home, so you can try it for free to find it out if works well for you.)
But, if you are dealing with one of those stealth viruses that prevents removal by anti-virus software (there are quite a few out there), then McAfee's free "Stinger" tool can probably get rid of it (I've found this tool to be very useful, but it doesn't have any automatic updater and it is NOT a replacement for a regular anti-virus product):
McAfee Stinger - Stealth virus removal tool (free)
Stinger will get rid of stealth viruses while they are actively running in your system, which is great because it means you don't always need to remove your hard drive to run an external scan from a clean system.
If the regular Anti-Virus solution and the Stinger solution fail, you may need to remove the hard drive and scan it from a clean system or use one of the reputable self-booting Anti-Virus scan CDs that are floating around on the internet. I believe Kaspersky makes one of these, but I've not had need to use this yet because the two solutions I listed above have always worked well for me.
The other possibility is that you're dealing with SpyWare, in which case you'll need a good SpyWare removal tool. Here are two that I really like, and which I've found to be safe and reliable (you should teach your relative how to use MalwareBytes on [at least] a monthly basis because it has a really simple interface):
SpyBot - Search & Destroy (free)
Note: Sometimes you need to run these tools from Windows Safe Mode, which requires a reboot and then pressing "F8" at the very start (before the "Loading Windows" logo appears).