David,
I had same problem. For me, the freezing occurs only when I previewed through Firewire. Assuming you’re working with NTSC DV and viewing through an NTSC monitor, try these things:
-Restart FCP with the camera already on
-Once up, make sure your Timeline window is active, and toggle the Firewire output by pressing Cmd-F12 a few times
-Resize your Canvas to 50%
-Also, close any unused sequence tabs in the timeline.
These procedures usually work for me. Let me know how it works for you.
Andrew