Just thought I'd post this...
Thanks to forum contributors I was able to figure out the format for the NSIM UNIX/X HP41 simulator ROM. If you have a copy of any HP41 ROMs in raw binary format (i.e., no headers/checksum/wrappers) I have a small program that will convert them to a format suitable for use with the NSIM emulator.
Basically, you create a text file listing the ROM image names and the starting addresses for each one, and this script will translate the ROMs into a text list file that NSIM wants to see.
It's a Perl script, written so as to be cross-platform usable (I wrote it on a Mac and tested it on a Linux box as well) and is rather simplistic but will get the job done. If anyone wants a copy, I'll be happy to mail it to them. It's very small -- about 60% of the script is documentation. I make no warranties, expressed or implied, but the price is right. And you have the source. :-)