I remember in the early days of my business how long it took me to remove viruses - about a 4 month learning curve to get proficient. Now I can do it in about an hour or so. And, yes, right now you need to take them back to your shop to do the work at a flat fee so you are not learning on their dime. It's also embarassing to look like a fool when a virus is kicking your a$$ when you try to do it in front of your customer.
Here are some partial Cliffs Notes:
Virus removal is simply a process of finding and eliminating the "offending" files and registry calls (unless it's a rootkit). If you remove the wrong file(s) you will cripple and corrupt Windows (don't ask me how I know). So be careful about which files you delete. You need to learn to spot bad files quickly and you will by more jobs you do. You'll also learn about the companies that are propogating this crapware.
Different visuses hide in different places and you want to learn how to find them and remove them in stages. First boot in safe mode, go to Windows startup (msconfig) and eliminate them there. Then empty the temp folders under each user profile in docs & settings. Empty out all the IE temp internet file folders under each user as well. Empty the temp folder in c:\windows\temp. Sort the system32 folder by date and go to the most recent dates and learn to distingiush between legitamate files and virsuses and remove or rename them. If you cannot remove or rename a bad file (now your hot) you make a note of the file name, boot to the windows XP cd (or Knoppix), and browse to the system32 folder in DOS (choose R for repair) and rename or delete the file there.
Reboot then run Hijackthis and delete any crap there (fantastic & important tool). If something keeps popping back into Hijackthis then you have a reinfector and you have to find and eliminate that. It usually means going into the registry to the Winlogon area and deleting it there.
Reboot and go to Add or Remove Programs and look for suspicious entries and remove them. Remove any instances of Norton or McAfee ... they are completely ineffective - I work on PC's every week that are heavily infected and Norton or McAfee are running and have no clue they're infected. Not only that you'll double the speed of the PC by removing them.
Install AVG, NOD32, Trend or other top ranked av app. Install and/or update Spybot and Ad-Aware (awesome tools). They will remove any files you missed during the manual removal and it will also clean out the registry (very important).
After I install these tools and update them to the latest definitions I usually start Spybot running on my way out the door of the customer's and tell them to run each one to completion sequentially and let them remove anything they find. I tell them this will take almost an hour for each of the 3 to run and it has to be done today. I only do this after I know the virus is gone and there is no evindence of it (popups, hijacked browers, etc).
Disclaimer: there is a helluva lot more technique, skill, and knowledge to successfully remove and eliminate this junk that I did
not post but this is a good start. If you do not know what you are doing the good old school of hard knocks will fininsh teaching you so back up important files before you start if you have any doubt.

I cannot over emphasize the importance of knowing which files and registry entries are legit and which ones are not. Screw up there and it's a windows reload.
BTW - You can back up data and reload windows in about 3 or 4 hours ... so being able to remove viruses in an hour is a good skill. But sometimes when a PC is heavily infected the OS is toast anyway so knowing when a cleaning will work and when one won't work is good skillz too.