I've found that trying to load BMP file is a good idea. I don't know yet how to use your TPixmap/TBitmap, but windows .bmp with 24bpp can be read almost successfully.
There are some problems with colors, no pallete support, but basic code is completed.
Besides, I've found that TCanvas.Pixels property doesn't work. I had to use line method, it is too slow. I think, this bug will be fixed. So, TODO:
1) Add pallete support -> ability to load 2/4/8 bpp files
2) Correct color support for 24bpp (it is a big problem for linux even through wine and GIMP)
3) Correct TPixmap support.
Feel free to fix anything.
I'll place sources of TImage components in some minutes. Then I'll send you the url.