Step 1-
Download Daemon Tools

Step 2-
Install it (duh)

Step 3-
Download the ISO (which would be the information, called an image, ripped directly from a disk)(again, duh)

Step 4-
Run Daemon Tools

Step 5-
Access the D-Tools menu, and go to "Virtual CD/DVD-ROM". Select a drive for it to mount (insert the virtual CD into), and find and select the ISO.

Step 6-
Run your emulator. Iit specefies which system it's for. Here's a REALLY good place for emulators)

Step 6-
Select the drive with the ISO in

Step 7-
PLAY! Oh, and in case of slowness... well, Youtube's your pal for that.