When importing PowerPoint slides as animations in Captivate 3, what is the
frame rate at which the animations are captured? Can the frame rate be changed?

I tried changing the project frame rate in Captivate (Preferences > Project >
Frames per second) before importing, but it has no effect on the actual
PowerPoint capture frame rate (the animations still appear jerky even if I
select 50 fps).

Captivate 3 is very limited in its ability to correctly import Power Point
presentations. By "correctly", I mean the transitioning to which you appear to
be referring. My only suggestion at this point is to check out Captivate 4
when it is available to the public to see if improvements have been made that
will address this shortcoming of earlier versions, with PPT import
functionality. Sorry I don't have better news right now. Larry

Regarding fps: The frame rate of imported PPTs is, I believe, 30 fps, the
default Captivate frame rate of display. I believe you are correct in assuming
that you cannot change it prior to the import. BTW, don't go over the 30 fps
anyway, as it won't help the problem you describe, and will probably cause
other problems such as excessive file size and issues with synchronizing the
project at play time.