Just in case there are other people out there using the GIMP, I have made a script that automates as many steps as possible when you are creating mugshots for facepacks.
It is your responsibility to make the picture square. Then, the script will:
<UL TYPE=SQUARE>
<LI>Resize the image to 95x95 (using the best possible interpolation)
<LI>Create a 1px frame in the colour you specify
<LI>Set the opacity of the layer to 99%
</UL>
To install the script, dump it in your local user script folder (~/.gimp/scripts on Linux, C
Documents and Settings\<user>\.gimp\scripts or something like that on Windows) and start the GIMP. Now, the script will show up on images in the Script-Fu menu under "FM 2006".
The script can be downloaded at
http://quovadis.dk/dl/fm-mugshot.scm 
Mugshot Script for the GIMP 
Linear Mode
