In order to use the DVD like a big floppy drive then you need something like Nero InCD. InCD allows you to use your rewritable disc like a big floppy disk. Copy files onto your disc using drag and drop or save them to the disc from other applications. click here I believe that you need to format the DVD first before you cab drag and drop files to it.
Nero Vision Express won't let you drag and drop files to your DVD, its for dreating movies. Have a look on your PC to see if you have InCD installed or have a look at your setup disc to see if you have it there.