First, Welcome to the forum!!
Your characters all have several files:
Erica.jpg
Erica.htr
EricaBack.jpg
EricaStart.jpg
The 1st one will display the Erica face from the character selections
The 2nd one is the 3D figure that appears in the Haptek command window or in the UltraHal character window when you are chatting.
The 3rd one is the BACKGROUND image for that character (this is the one you want).
The 4th one is shown as a startup image.
Simply locate the jpg file you would like to use and RENAME it to your character's name. Be sure to use the word Back in the file name.
For example:
You have a character Catseye.htr. You should name your background image, CatseyeBack.jpg
You can also rename any of the other characters that you don't wish to use like Erica or James, etc.
Hope this helps a bit!