Simpletext, eh? I vaguely remember that, sort of a wordpad like tool.
Well, I think your best bet is to load the image into a package on the mac - anything that can export it again in a more accessible format such as jpeg, png. Even PICT, as used pretty much only under MacOS can be imported by many PC applications. So it may be you are forced to convert the simpletext image format to PICT (assuming you don't have any other mac applications handy), put it on a PC floppy and load it into photoshop or paintshop and export it again as jpeg or whatever.
Hopefully, you can just export it as jpeg straight from a suitable mac application.
For the purposes of submitting to amiga.org, I'm sure jpeg or gif are the best choices. Not sure if png or other formats are allowed or not.
