Here is a way to make a blank floppy disk image that you can use in Oracle VirtualBox. It's a hacked around version of this. You just make a batch file with these DOS commands in:
if exist blank.img del blank.img
for /l %%i in (0,1,31) do echo 01234567890123456789012345678 >>blank1.img
for /l %%i in (0,1,35) do type blank1.img >>blank2.img
for /l %%i in (0,1,39) do type blank2.img >>blank.img
After running it, you end up with a working disk image, and here is a version that I then reformatted inside a virtual machine. I've since found that you can use these images in Windows VirtualPC too, although there is no UI to attach them, you have to edit the xml files of your virtual machine manually.