Creating an image file

I want to burn a CD from files that are on networked computers. I can’t rely on the speed of the network at all times (I want to prevent underrun) so I want to first create an image file, and then burn the image file. I see that I can select the Image device as the output device, but the default output is to the source directory. How can I output the result to a local directory?? Should I be trying to figure out how to build my own image file? Is there information anywhere on how to build an ISO image file?
Thanks! Istar:)

www.winiso.com

or you can open nero and close the wizard. Goto recorder at the top and select Save Track.