All of these tools can perform screen capture.
windows media encoder (wme) - free, records to wmv files,
Camtasia - $300, records to anything but most notably to Flash/swf/flv, includes Flash player which can be embedded in a website,
Captivate - $600 alone or more as part of Adobe Premier Pro, said to be a memory hog, very "cool" output Flash player (embeddable of course), integrates well with all the other Adobe products for a very smooth experience (efficiency)
Snapz Pro - inexpensive tool for native video capture on a Mac.
For me, WME is out because I need to be able to produce "smart" (interactive) video.
If I was going to be using a high-powered computer, it would probably tilt toward Captivate, but since I need something light on memory, I'm leaning in favor of Camtasia, which is a very nice piece of software compared to everything else.
Here's another big "problem" with Captivate. Adobe is very clever, and they've structured their prices so that you are strongly encouraged to buy Captivate, for example, as part of one of their packages which can be purchased at discount in a mega-package ... you get the idea.
Last year I bought a $100 flash-building tool which was terribly inefficient and ultimately I couldn't get motivated to produce anything.
I'm going with Camtasia for now. Leave me a comment if you'd like an update on my experience. I usually respond within 24 hours.