Q: New to FCE 4 - How to get smooth playback in Canvas

I'm new to FCE, but not new to video editing software.  I've used everything from iMovie to Adobe Premier Pro, and have never experienced this issue.  I've read the manual, I've searched online for help, but can't seem to find the solution.

Once I move a clip from the Viewer to the Timeline, viewing in the Canvas is choppy.  I've tried to adjust the real time settings, I've used different types of video files from different camera sources, nothing works to give me smooth video playback in the Canvas.  The only thing that does work is "rendering" the Timeline, but that can take hours depending on the length of the sequence...there must be an easier way?  I am working with a new iMac, 3.4 Ghz, 16 GB memory, several TBs of hard drive space, no other open applications.

It is very difficult to edit a sequence when the playback is choppy, and way too time consuming to render a sequence before I've even really started editing.  If somebody could point me in the right direction, I would be very grateful.  I'm not the most tech savvy, so directions/instructions need to be step by step and clear, and any video tutorials to fix this exact issue would be awesome, but I would appreciate any and all suggestions.

Thanks.