Hello,
Probably you know this by now, but if you don't, for "compressing" a CD/DVD image you can use ULTRAISO like this: under menu FILE / PROPERTIES you will have the properties window of the image you want to create; right from where you choose the media type (650MB/74min; etc...) you have a checbox named "Optimize". Check-it and in the CD/DVD image if you have 2 or more identical files included in your image then those will be written physically on the image only once with 2 or more links to them.
Hope that will be usefull to you.