Going back to general performance, this relates to anything in general. It also equates to AH online play. If you have too much garbage installed and running on your PC before you load anything (when you're just sitting, looking at the desktop) you can suffer big performance drops or FPS skips.
When you are NOT running anything special, just sitting at the desktop, hit CTRL ALT DEL, and at the bottom note how many processes you have running. Mine shows 26 and that's with MSIE up and a couple others I could kill if I wanted to.
If you have 35 you're in trouble. If you have 40+ you're up a bleepy creek. If you have 60+ you probably have a Dell and are in deep Bantha Poodoo.
It doesn't matter if you have 4 gigs ram, the best Core2 Duo chip overclocked to the fastest speeds. If you've got 60+ runnin when idle you're going to feel it.
So if you have these problems (skips when capturing film) make sure nothing else is running in the background. Not messenger. Not mail. NOT anything from MS office (including the fast-start toolbar). Not any active desktop that might randomly rotate your backdrop while you're working, or anything.