Well, geeze - I don't know. Whats the file extension now? If it's not already an ISO then I assume it's a zip, or rar file of some kind. In that case you would need a decompression program like winzip or something to uncompress it. Then it should be the ISO file after being uncompressed. Then you would need a good burning program like Nero to make the bootable image file. You can go here
http://iso.linuxquestions.org/ and see how to burn an ISO.