I recently had to convert a batch of Interleaf files to FM using Frame's FilterPak 3.0. The filter requires IAF (Interleaf ASCII Format) as input and outputs MIF. Because Interleaf supports some functions that FM does not, you may have to search for key words in the IAF file and remove them. (The FilterPack docs list a few of these. I can provide the other ones if you need them.) The only other difficulty I encountered was not having enough memory and/or temp space on my local hard drive (running FM 3.
1X under UNIX). I found it necessary to use an ASCII editor to split up large IAF files into smaller files that the iaf2mif filter could process given the limitations of my system.
The filtered files needed some further formating, though. But that may have been due to the fact that the original writer didn't know how to use Interleaf very well.