It's an idea that will work, but it's not worth the trouble.
Download Puppy Linux 4.1.2 (be sure to get that version, NOT 4.2.1) at a friend's house and burn the image to a blank CD. DON'T just burn the file to CD, you have to burn it as an IMAGE, or it won't work properly. All CD burner software that I know of offers that functionality, and if you are in doubt, use Burnatonce (freeware) because that's all it does.
Once you do that, connect it to the Internet with the "Connect" button, then download the Avast! for Linux Workstations from the Avast website with "Browse" from Puppy. You want the tar.gz version.
Right click on the file in the Puppy Explorer "File" and select "Window" > "Terminal Here" then type in "tgz2pet avast4workstation-1.3.0.tar.gz" without the quotes. The file icon in the explorer will change, and clicking on the newly improved icon will launch the self-installer.
Once its done, type "avastgui" without quotes in the console and hit enter. It will ask for a key. Put your Avast! registration key in the box and hit OK and it'll load up Avast for Linux. Tell it to download updates.
Poke around with the icons at the bottom of your screen until you find the one that contains the WINDOWS folder. Then in Avast choose "selected folders" and type in /mnt/**** and change the asterisks to the Linux name for the partition your WINDOWS folder is on (sda2 on most OEM installations.) So it would be set to scan /mnt/sda2, for example.
Then let it scan! Basically this lets you scan it AS IF it were in another computer, because you have a second fully-functional OS and virus scanner looking at it, but you don't have to buy anything more expensive than a blank CD. If you read the link I provided you with earlier, we worked through the whole Linux thing already, although using a different AV program that is good, but not quite as effective.
Once you get the crap off, you might still have to do a repair installation of Windows to replace any missing files that the virus ate, or rather that the virus caused Avast to eat. Avast would rather you go without the file than use an infected version.....and I guess I would too!