Hi,
Edted because of incredibly crap "copy and paste" technique

Using High Density Floppy Disks as Double Density Floppy Disks can give you trubs. The Magnetic layout on the High Density Floppy is different to the Double Density Floppy Disk and you will most probably loose all your Data at a critical time.
Some peeps have reported that they have had no trubs using High Density Floppies formatted as a Double Density Floppy Disks, but, I still think it's an "emergency" method only, and also make sure you've backed up your Data before using the disk.
I hope this helps you.
Regards, Michael
aka rockape