Hmm, if they are .bmp then (I didn't have time to check) then they may be using dts compression.
To get this dtx formatted .bmp into a 32 bit color, you'll need to use Imagetool or DTXbmp to edit and resave them in 24 or 32 bit color .bmp format. Imagetool gets installed with Gmax (which is on your FS2004 CDs) into the FS2004 gamepack plugins folder. DTXbmp is free, and is avaliable on the web for download. Here is a link to DTXbmp, thanks to HH!
http://www.mnwright.btinternet.co.uk...ams/dxtbmp.htm
Post back if you need more help, I know this conversion process well!
As for PSDs, I met the same trouble when I did some repaints, sorry about that. They seem very rare compared to the IL2 world.