This is a topic I wrestled with long ago. Unfortunately, I think you may be out of luck. I have a Mac Classic as well, and it only has a double density floppy drive (720k). There are some apps for windows that can read and write high density (1.4MB), like
Gemulator Explorer, or my favorite,
HFV Explorer, but it's impossible for a PC floppy drive to read or write a low or double density mac floppy. The only solution I found was to acquire an "newer" older mac, like one of the LC series, with a high density floppy drive, and transfer files from the high density floppy to a low density floppy there.
To add to Aaron's post, I believe PC Exchange was first introduced in System 7.5, and did allow Apple to read and write PC floppies. I've used HFV Explorer for a while to transfer files back and forth to my little LCII, then used the LCII's floppy to transfer files to a double density disk readable by the Classic.