Guis,
Unfortunately, CFS 2 will only recognise 16 bit 256 x 256 extended bmps.
Both Dvslats & myself have used some of Aimes excellent work, so it's a good choice of start point.
you might find the bitmaps get a little speckly & "busy" looking once you've reduced the size to 256 x 256, but it's worth having a go.
For info., here's the method I use.
I use dxtbmp & open as a normal 24 bit bmp, then export the image to PSP.
I adjust/ modify & reduce size to 256 x 256.
To make into a format CFS 2 will recognise you'll then need to use BMP2000 (again from Martin Wright:salute

to create the extended bmp set you need.
Often I use an existing bmp with a similar pallette as a start point, then import my new bitmap & create the image set within BMP2000.
Hope this helps