Doing it thru Paint the way I said assumes that the original file is 300dpi. If it isn't, then you have to use the Scale % to adjust the sizing up or down accordingly.

Also, depending on your printer's margin tolerances and the size of the cover, you might be able to get away with leaving it on "letter" size. You'll have to experiment with that for yourself. If you're printing a wide DVD cover, anything bigger than your standard Amaray size, then you have to hit "legal" and print on legal size paper no matter what.