To burn an ISO file to a disc in Windows, simply open the file with your favorite burning software. If you don't have a particular CD/DVD recording program, you can download the free Infrarecorder software
here. For Windows 7, you will need a blank DVD.
Once the disc is burnt, be sure to run Boot Camp Assistant from Applications => Utilities on the Mac.
This is key: When prompted, print out the documentation for Boot Camp. It is essential to read through and understand it before you proceed. Additionally, it is STRONGLY recommended that you backup your data before you begin. Any time you make a major change to disk structure, it's important to back up as the risk of data loss is higher than normal.
If you'd like to take a look at the instructions before hand, they are also available
here.