Read http://forums.cnet.com/7723-7592_102-551621/panasonic-hdc-tm90-mac-hd-editing-question/ where we looked at this camcorder and issues with iMovie 11. My bet is your older iMovie only makes the issue worse.
The last time I checked that upgrade was 12 bucks. Maybe it's still possible and you can see what we covered in that discussion.
Beats having to go up to FCP.