When I installed Final Cut Pro v. 4, I lost all ability to Log and Capture. Not just in Final Cut v.4, but also in the older version 3 which was left on the drive by the install. When I would open the log and capture window, FCP would unexpectedly quit every time.

I trashed preferences according to instructions on Ken Stone's site,

(CLICK IMAGE TO VIEW FULL SIZE. Thanks to Ken Stone for these instructions!)

I then uninstalled Final Cut 4 and 3 according to these instructions on Apple's site, uninstalled iChat AV, just in case, and finally reinstalled FCP 4. It still did not work. I finally did a clean install of the system, and reinstalled Final Cut v. 3, which started working again. At this point, I happened to search MacFixit.com about this issue, and it turns out there is a known issue with IOXperts webcam drivers and the log and capture function - although this was with Final Cut 3. I had those drivers installed and now think they may have had something to do with this issue. I will be reinstalling FCP v. 4 soon, and will find out for sure.