Hmm...  What kickstart/workbench revision is your system?  CrossDos was included with Amiga since revision 2 AFAIK?  (Never really had AmigaOS2, had 1.3 and 3. 

)
Another thing you *could* do is get a CatWeasel Mk3 for your PC.  Then you could plug it into a PC drive and write floppies in Amiga Format that your A500 could read.
I don't know if the Catweasel comes with software to write ADF's into Amiga format, but you might be able to use it Amiga software via an Amiga Emulator on your PC.
Otherwise, I'd say if you can try and track down an external floppy drive for the amiga.  Then you can possibly have a boot disk with basic workbench, term program and a program to convert ADF's and then a blank disk in your other drive.  Then you could connect the PC to the Amiga with a null-modem cable, transfer the file over by dumping it to the amiga floppy (if it can fit) otherwise you might have to have 2+megs of ram and setup a ramdisk and save the ADF transfered to there.  Afterwhich you conver the ADF to floppy.  
Seems like a lot of bother.  Would be easier with some sort of harddrive attachement. 
