Anyway... few discoveries...
First, its possible to change the bmps that show up for each month as a background.
My first test was replacing the image with the same size and such (60x34 pixels). The result:
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Ok, now, anyway. As this is cool and all, it looks like completel crap. It stretches the shoddy quality image to 480x272, and it looks horrible.
So, i poked around a bit and noticed that there was still about 10k left in the 16k cluster that the 11.BMP (November background) was in. After some thought i decided to do a test if a larger image would work.
I couldnt fit double size (120x68) into 16k, so i went with 1.5x (90x51).
Wrote the code to change the filetable entry to reflect the new 13k'ish size, and write the new bmp to the flash.
Well, after sweating for a minute or two... the result:

It worked! The PSP took the higher res image and made it full screen! Granted, its not THAT much better at 90x51... but the fact that the size isnt fixed is good.
Heres the bmp:
http://www.skie.net/test.bmp
After I finish my fat12 driver for lflash, i'll work on making a full 480x272 one to test.
Anyway... some good info I guess.
Enjoy.
-Klim
P.S. - Sorry for the bad quality pics... i dont have a good digital cam at the moment.