Can you give us a bit more info? Is this purely decorative, or do the arms serve a function while the computer is on?
You could use servomotors, but they can be a bit pricey. Sites like
http://parallax.com sell them, although if you're in the US and don't want to pay shipping, I've seen servos for the VEX kit for $10/each. (Darn you Americans and your good electronics stores... just kidding
![Wink ;)](./images/smilies/gear_wink2.gif)
I would note they have a nonstandard pin order on the cable, so don't just plug them in according to a general pinout.
Do you have a laptop or desktop? Which part of the computer are these going to be mounted on?
Also, what interface to the computer do you want? A COM port would probably be the simplest, since USB requires a hefty (e.g. $1500, I think) fee every couple of years for a Vendor ID. It also has good programming support.
Do you have any programming experience? It likely wouldn't be too hard to do, but there aren't many people who would have the time to code something for someone else's one-time mod. (at least for free)
What microcontroller do you want to use? If you have the budget, a Basic Stamp (see the Parallax site) would be by far the easiest. I've also seen them in US Radioshacks, and RP Electronics in Burnaby, BC (right next to Vancouver). If you want something cheap, you can get PICmicros from
http://microchip.com for a couple of $$'s, but unless you have one of the few computers with an up to spec voltage COM port, you'll have to spend at least $50 on a USB programmer, or pay them a bunch to pre-program it. There may also be someone online who has one willing to program it for you. If I had the time, I might be willing to do that, but no promises... If you have a non-free e-mail address (e.g. academic or corporate) you can actually get the PICs free from
http://sample.microchip.com
In general, how much electronics experience do you have?
If you give us some more info, we can probably figure out something, but I'll have to presuppose some knowledge of the concepts.