Question about .dmg files on Macs & downloading them?

Hello, i am wondering/looking for a way to download a .dmg file onto my Windows Vista computer, and mounting it there so i can convert the file into a .rar and USB it to my Mac. My Mac's .dmg system is bugged, it says it cannot mount anything, is there any way to avoid mounting .dmg files at all? Or do they indefinately have to be mounted. Please do NOT post soultions to my Disk Mounting problem, i just want to know if you can get around .dmg's.