you could OPEN the .img file with WinISO and convert/save as an .iso file.
OR (hey I am on a roll here..)
you could "mount" the image to a virtual drive using Daemon Tools (its a freebie, do a google search) then just do a copy cd from the virtual Drive to your CDRW. This is an easy foolproof method to make copies.
...there are any number of ways to convert from one .this to another .that-- If you want to do it the hard way just ask.