Whenever I try to do a screencast my pc lags or freezes

[rabidsushi]

Every time I press the record button on any screen recording software, my computer either freezes for a while or lags until I kill the program after around 20 presses of the 'stop recording' button. This is extremely frustrating, seeing as a lot of people have seen screenshots of my desktop and want to know how I got it to look the way it does, so I need to do screencast tutorials. I am currently operating on a new 32x Sony Vaio NW series laptop with an ATi Mobility Radeon HD 4500 series graphics card that is hooked up to an acer h233h HD 23 inch monitor as a dual screen.

Please Help