how to run ROM?

i need a program that allows me to play ROM files or allows me to convert a rom file to a smd file...i run windows so i need a ROM emulator

look at emulator-zone.com and choose the emulator there

What kind of file are you trying to convert from?

SMD files are used by Sega Genesis emulators.

uhhh how do i open dmg file? or with what?

DMG files are compressed disk images for MAC. MacOS can simply mount them if you double click but I dont know anything about windows.