Problem with connecting the drive to another machine is that many times, during the scans you will blow away system files, so you put the drive in the other machine, and it may work, but half the OS may be gone too.
If you've never heard of this, try it, use it. You will love it!
http://www.ubcd4win.com/
It's the Utlimate Boot CD for Windows. You need a Windows XP or Server 2003 disc(I think that Server 03 works) to build it. Once you build it, you can have it make an ISO you can burn on cd, then when you find a computer you can't boot, many times you can boot a copy of Windows XP from the disc you build. I use it for data recovery if a pc won't boot, hook my external to it, boot up, beautiful.
I find it useful if I'm removing viruses and a hosts file is messed up and hidden to where I can't work on it in the regular OS, boot to that CD, which usually lets me see it, take ownership of that file and delete, and I can then replace it with a clean hosts file.
Also, there is a program on that disc called Darik's Boot and Nuke. If you've got a drive you want to erase or rescue from viruses, that app is supposed to do a Department of Defense grade data wipe on the drive.
It's a beautiful tool. I've used it when machines would not boot due to malware, go in and run a disk check on the drive, get the machine booting back to safe mode, and then remove things. You can do stuff like that, people think you are a magician with pc's, lol.
Btw, Avast gets my vote also. Used to use AVG, decent software, but another friend of mine who's also a tech recommended Avast. I tried it, not going back to AVG. Avast, even in the free version, has too many features. Of course real time scan, web shield, etc. One of my favorite things with Avast is their boot time scan. You can basically have the scan intercept the pc before it can boot and delete things that may have stayed hidden from other apps. So far I've not seen another Antivirus able to do that.