Just a quickie - I didn't know this and it may be a bug/feature specific to PE4.
Create a linear gradient on an object in the titler. Then select radial gradient. Choose a number of repeats (say 3) then change back to the linear gradient. The linear gradient is now repeated the same number of times as the radial one.
It is of course at this point someone details how to do this in the linear gradient screen and I've just missed it....