To burn an ISO disc image to a CD or DVD in Mac OSX you need to do the following;
Go into Disk Utility (Go, Utilities and Disk Utility in the finder context menu.)
Open the ISO image you want to burn with Disk Utility (via “Open with” in the finder context menu.)
Select the image in the drives list in Disk Utility.
Hit the “Burn” button and insert a blank CD.