Okay ill throw in my 2 cents...
Hope you dont mind I decided to take the time to write all this up I hope this will help you with your adventures with FPSC
First off you should get to know your FPSC Directory
C:/ Program Files/The Game Creators/FPS Creator
Most of your textures but not all of them are usually located in the texture bank directory
C:/ Program Files/The Game Creators/FPS Creator/Files/texturebank
Footnote:
In your segment and entitybank are files called .fpe and .fps these are script files for your models you can open these files with your notepad and in these script files you can see what directory your texture files are setting in.
Okay you found your file now what do you do.
Well here is where you need an image editor
Suggested image editors are
My top pick is Corel Paintshop Pro (Better known as Jasc)
http://www.corel.com
My next top pick is Adobe Photoshop CS (Expensive to most people)
http://www.adobe.com
A good image editor Gimp (Free and has a DDS plugin)
http://www.gimp.org
For me I make things easy on me I like to use this program called DDS Converter 2 this allows me to change the image format to a format thats easier for me to edit. Best of all this program is free
You can find this file here
http://eliteforce2.filefront.com/file/DDS_Converter;29412
Okay got your image editor and converter now you take your dds file convert it over to say a jpg format use your image editor to make your changes (Sorry can't take the time to tutorial the image editors here) save your file now use your converter to change it back to dds format then swap it from the original file (be sure you back up the original incase you want to change it back) then run your game and see your changes
If you think education cost so much you should see how expensive ignorance can cost you