Kathy,
close Firefox, and, then go to Start|Run|"C:\Program Files\Mozilla Firefox\firefox.exe" -p , with a keyboard space after the final quotation mark. If you enter this, the profile manager will come up. You, probably, have only "default", on the write side. On the left, there are three buttons, one is "Create Profile". You want that one. Enter any name other than "default". Even "default1" is ok. The path can be anything you want, including the Desktop.
When you are done, you can write click|Properties, and append the Target line with -p default1. You should have: "C:\Program Files\Mozilla Firefox\firefox.exe" -p default1, with a keyboard space after the "p". From now on, Firefox will open in "default1". Play around with it, and if you don't like, you can always remove the "default1".
I use the same desktop shortcut, and, if you choose to leave out the extra direction, you can select the profile which you want, when you want it. I would uncheck the box under the profiles list.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1