button pusher thingy

Hello,
I am new to the robotics field and i have a question.  My friend has
one of these things that he found in a printer that when you run a
current through it, it pulls the rod down and when you disconnect the
current, the spring pushes the rod back up.  See photos for linked
below to deal with my crappy description...
Just for kicks, I wrote a guitar hero playing computer program, and I
want to make it into a robotic mechanism.  See the pictures for
details.  I am wondering what it is called and if there is any other
better (and cheap) parts that can work with my project.

http://farm1.static.flickr.com/207/493354668_48832d8e4a.jpg?v=0
http://farm1.static.flickr.com/224/493354660_cd1ff88f15.jpg?v=0
http://farm1.static.flickr.com/232/493354636_9193be1769.jpg?v=0

Thanks!