A) Search CPAN to see if it has already been done. If so, use it and you're done.

B) If the format has some documentation:

1. ) Look up documentation to understand the source file.
2. ) Convert the file by hand once to be sure you understand it.
3. ) Write function to do the same thing you just did by hand.
4. ) Upload it as a module to CPAN

C) If there is no documentation:

1. ) Create a few of the simplest possible sets of data you can make, and save them.
2. ) Open the files in a hex editor and compare them in order to figure out how the data is arranged.
3. ) Repeat from Step 1 until you understand how all the features you care about are saved.
4. ) Convert the file by hand.
5. ) Write a function to do the same thing.
6. ) Upload it as a module to CPAN.