I have an unmodded fresh copy of CFS3 installed in C:/Users/Me/CFS3 for use to install other mods.
I have a modded copy of CFS3 installed in C:/Users/Public/CFS3 to play which included Firepower.
I want to install another copy of CFS3 to use for BoB but I can't get anything but PLAY or Uninstall when I insert the CD.
I removed the registry key but that didn't help.
How do I get another copy of CFS3 installed? How do I keep windows from recognizing the other copies of CFS3 already installed?

Richcreator, this is how.
Simply make a copy of your vanilla, fully-updated (3.1 and 3.1a) CFS3 install, right where the original is located is good.
Rename this Copy of Combat Flight Simulator 3 folder to an appropriate name.
If you have ETO installed, go into that main game folder and look for this file: MultiCFS3.exe.
If you don't have ETO installed, go here:
http://www.mnwright.btinternet.co.uk/
On the home page, look to the left for a list. Find CFS3 and click on it. On the next page, click Utilities in the middle of the page, under the picture. Click on Multi Install in the list in the next page. On the next page, you will see another list. Look for MultiCFS3 on that list. Click on the yellow dot next to it, and download the file.
Once you have MultiCFS3.exe, place it in the copy of CFS3 you just made, and run it. It changes the name with regards to the folder that will be created in your Application Data folder.
I can already tell you that if you had two installs without changing the name of one of them with regards to the Application Data folder, you may be having problems with the two installs you already have, as both installs are using the same folder in Application Data.
You can fix that with no problem by simply putting a copy of the MultiCFS3 in the Firepower install and use it to rename that install, too.
I hope this helps.:d