Step 2: Get rid of that virus.
If your non infected pc does not have antivirus installed, see this: http://www.ngook.com/archives/34 . 
If you purchased the recommended adapter your steps are, plug adaptor into hard drive, plug usb side into noninfected pc, plug power into hard drive.  Wait for windows to detect your drive (and do a brief scan so it knows whats on it).  Skip to step 3.
If you did not purchase the recommended adapter(and you are working with 2 desktops, or the infected pc is a laptop and you have the appropriate adapter to connect it to your desktop) then you need to turn off the non-infected pc, open it up, and install the second hard drive.  Also, your board needs to support the type of hard drive you are plugging in.  If you pulled a sata drive out of the infected machine, and you only have ide in the non-infected machine, then you will need either the mentioned adapter or another non infected computer.  The adapter really is the way to go. It is not necessary to “install” the infected hard drive into the non-infected pc, just connect the necessary cables to it and set it where it won’t fall and where the circuit board wont touch metal (ie, a piece of cardboard works well.  Boot the non-infected pc.  Once you can see the infected hard drive on the non-infected pc, move onto step 3.

Step 3: Scan infected hard drive.
DO NOT ATTEMPT TO ACCESS ANY FILES ON YOUR INFECTED HARD DRIVE.  The whole point is that you can boot up the pc without loading the virus.  If you play around on the infected pc and get your non-infected one sick, then you are in the same boat but you now have 2 pc’s to fix.  Fire up your antivirus software and run a scan. Direct it to scan only the infected hard drive.  You can scan the whole computer if you want (ie you are going to bed and you haven’t done one of those in a while) but they take longer.  Optionally, you can run an antispyware scan with spybot S&D as well.  If your antivirus does not find anything (rare) then run the spybot scan for sure.  If you don’t know how to run a scan on specific parts of your computer, run a google search or check out your antivirus company’s website.

If your software found viruses (and cleaned them), congrats, you are probably done.  Put the hard drive back in the original pc (using proper grounding techniques) and turn it on.  If it boots, then yay, you are done.  If you get an error booting to windows, then you will have to wait until I get my guide on repairing windows installations up.  If it didn’t find viruses, then try a different antivirus software.  There’s plenty of free ones out there.  Good luck.