Don't use windows movie Maker to actually shoot or compile your animation together. You should use a program specifically designed for stop-motion animation purposes to actually compile your movie, then edit your larger clips afterwards in a video editing program like Windows Movie Maker. An animation program will make it easier to arrange, re-arrange, add and delete single frames. Typically, playing around with multiple single frames is kind of difficult and bothersome in video editors since they weren't designed with frame by frame animation as a primary function in mind.
To actually frame-grab and compile the movie, I'd suggest using Monkeyjam if you're on a PC. It's free.
http://www.giantscreamingrobotmonkeys.com/monkeyjam/
AnimatorDV: Simple+ became freeware.
http://www.animatordv.com/download7
If you're on a Mac, you could try Framethief or FramebyFrame.
http://www.framethief.com/
http://web.mac.com/philipp.brendel/Software/FrameByFrame.html
Download one of these programs and install it. Once you start the program, it should automatically detect your plugged in webcam and you can start using the software to take images and turn it into an animated video.
And you really shouldn't be using Play-Doh. Plasticine is preferred, as it's a type of modelling clay specifically designed not to dry out easily. As such, if you do use lights while you're shooting the heat won't dry out your figures (although they will become soft and limp, that's normal with any putty). Don't use Play-doh, it becomes too brittle too quickly.
Usually art stores sell cheap bricks of plasticine, along with higher end stuff, like Van Aken and Roma Plastelina. The cheap stuff will do fine if you just want to experiment and make your own films. I've found the cheaper bricks to be fine for stop motion animation. Van Aken is very soft, too soft I found. It's definitely too soft if you don't want to use armatures. (wire skeleton inside your character.)
Let me know if you need any more help or info.