Do not underestimate this cost! My current DVD Project requires about 3 Gigabytes of RAM, bringing the machine well over the 4 Gigabyte border:
My recommendation: If you really want to use Dynamic Link, get a 64-Bit Operating System and as much RAM as your machine can handle. All CS4 Applications may be still 32-Bit (with the Exception of Photoshop) and thus limited to 2 GB per Process, but running 10 or 15 of those 32-Bit Applications will still fill your memory. Yet on the other hand, not using Dynamic Link seems now like loss of flexibility, because the integration between Premiere Pro, Encore, After Effects and Photoshop is excellent in CS4.