Chances are slim, but you still can get a virus. Just in case, make sure you have a protection program such as Virex or Norton Anti-virus . Most of the demos come directly from game companies, and are virtually virus free. It has been over a year since I've gotten a virus from a download, but it can happen, so be careful. I've downloaded the file, but I can't get it to work.
Most files are in .zip format.
I've unzipped it, and installed it, but the emulator still doesn't work. After installing most emulators, you still need to download a ROM of your favorite game. Links to ROM sites are at the bottom of each emulator page. Roms are copies of the original games, but in file format. Since you can't put a Super NES cartridge into your computer, someone who has more technical knowledge found a way to save the games on the computer.