First of all, you'll probably need PC Exchange installed on your 68k Mac. If you're using System 7.5 or higher, you should be good.

With ShrinkWrap 2.1, you can create an MS-DOS Image File from a floppy. Check the Preferences screen to ensure floppy disk images are saved in the correct format, then use the 'Create Image from Disk' option to (surprise!) create an image from your DOS floppy. Copy the resulting file to your Vista PC with whatever method you prefer (only the data fork needs to be copied).

Back in Windows, you can mount the disk image using ImDisk. Just click 'Mount New', select your image file, verify that ImDisk recognizes the file system as FAT, and if all went well the disk image should appear as a new drive in Explorer.

P.S. The link where I originally downloaded ShrinkWrap 2.1 seems to be dead now. I'll see if I can find a new download link for you.

[edit]

This one seems to work: ftp://ftp.uni-koeln.de/mac/Utilities/installing/shrinkwrap-2.1.hqx