Scrub timeline ?

Hi All

What I am trying to do is scrub the timeline while recording it --
I used to be able to do this with FCP 3.4 on my old G4--
The scrub would record smooth and looked good--

After upgrading to FCP 4 (G4)
I could still scrub the time line and record
but I had to Trick FCP by selecting print to video and canceling-
to get this to work

Now with FCP 4.5 and G5 dual
when I scrub the timeline and record its real choppy and studders--
and really dose not work anymore

I have footage of a puppet on a string that I am trying to smooth
out it's movements and make the movements look more realististic-

Any idea how I can get this to work again--
maybe I have some settings wrong ? --Thanks --Jay--

What about using the 'L' key to run it in fast forward? Is this smoother? You can get up to four times faster based on how many times you hit it.