I have been curious for the past few days if it were possible to get information out of imp format files without using the eBook Publisher software from eti. The api that they provide seems to be full featured and has let nick do some wonderful things managing the imp files. The down side of that, for me at least, is that you need windows for most of it to work.
So being curious I pulled out my Camel book and decided to wade around and see if I could get some of the information out of an imp file. The attached short script is the beginning of what I've been able to extract from unencrypted books so far. There is more but this is pertinent for sorting and searching through a collection of imp ebooks that might have gotten just thrown into a directory with none too descriptive names.
Location of the information in the file came from
http://www.chromakinetics.com/REB1200/imp_format.htm