d64 is one of the PC specified file types for Commodore emulation (along with t64, g64, taps etc). This one relates to a whole 5.25" disc.
Assuming you have a formatted floppy in the 5.25" drive, put the cursor in the C drive window and position it over the xxxx.d64 you wish to transfer (be in Gremlins or whatever). Now press Alt F5.
It should come up with a window saying "copy xxxx.d64 to 8:" or something similar. As you are copying to device 8 (and not the C drive), you don't need to specify a destination name, so just press Enter.
Hopefully the drive should now whir away and it should show the disc image being copied track by track to the real disc...
If you just want to copy individual programs (PRGs)... then press right cursor on the d64 file to view the track listing. You can then select the prgs you want by holding down shift and moving the cursor, then press F5 to copy these to the floppy. The default destination name is the same as the name on the image, so just move to Yes to All and wait
- for all your cartridge needs!
"My aim is to produce games that have graphics and audio that will rape your eyeballs and take your ears from behind with a strap-on" - Jeff Minter