Saving .IMA files...

Lately I am messing up with bootdisks and I'd like coding a small command line application that takes as parameter
a folder,
a .bin file as boot sector,
a size type (1.44MB or 2.88MB essentialy),
and output a .IMA files keeping all files of the folder with the .bin file as boot sector.

That program would be analogous to MS cdimage.exe that outputs a .ISO file.

So, my problem is, does exist a info page about .ima files? Or how can I know where to puts the file's contents for making a valid ima file?

Actually, this question may be extended about every format.
How do you know how to save corretly a known file format? Like a .jpg, or a .mp3 file?

Thanks

http://www.wotsit.org/

WOW, it is *really* great. Thanks a lot.