My little plastic white macbook with 2.4 dual and 2gb ram edits HDV like it's SD. I bought the thing against all advice ("only the most expensive macs can edit hdv!!1!!1") and I haven't had any problem with it. I'm editting HDV (in the train!) on a portable harddisk powered by the firewireplug.

If fcp acts strange with HDV, it's settings most of the time. Make sure you easy-setup in the format you want to edit. That's most of the time the only thing that needs to be done.