It has been asked before, but dont worry! You need either Imagetool, or DXTbmp to open the bitmaps.

Dxtbmp is available here: http://www.simviation.com/fsdesign_utilities.htm

Imagetool can be can be found on other fs sites I believe, or a quick google should find it.

Just a hint to keep you going in dxtbmp, the files you cant open in photoshop etc are Extended images, regular bmps are 24bit, and FS will accept DXT3 (compressed) and 32bit (uncompressed) bitmaps only.

Hope this helps, feel free to ask more questions if you need to.