You may not be aware but Apple has a feature where you can share a disc in one computer with another. That means you use the DVD drive in the portable and share it over a network connection with the iMac.
Having said that, the CS3 installer has problems with the newest versions of OS X. I was running CS3 until recently when I gave in and upgraded to CC. The current software is 64-bit (so it takes advantage of having more than 4GB of memory installed in the computer) and has a lot of new features.
My recommendation is to leave CS3 for an older computer and older version of OS X and upgrade.