From Nero Burning Rom help file:
Creating an image file
Here is a step-by-step guide to creating an image file using Nero:
From the Recorder menu select the command Choose Recorder and select Image Recorder (and not the currently installed recorder). Then confirm this selection using OK.
Next create a CD-ROM or audio compilation as described in the appropriate sections.
Click on the Write CD button or select the Write CD command from the File menu to open the write dialog box.
Note: If you are unable to click on the "Write CD" command the compilation window is not the currently active window. To correct this: please click on the compilation window to activate it.
The Write CD dialog box will then open â€“ the procedure is the same as for producing a new compilation but the Burn tab is now in front.
You will be able to activate only the "Burn" action because you are producing an image file.
I know this cant be hard but where is the Write CD command or button? (Maybe I need more coffee. heh)