Hi,
I've done a quick search on education.com and there are plenty of science activities involved magnets. here are just a few:
 
Measuring Magnet Power:
http://www.education.com/reference/article/science-measuring-magnet-power/
 
Magnet and Heat:
http://www.education.com/reference/article/Ref_Magnets_Heat/
 
Or you can see other ideas from my search results:
http://www.education.com/results//?q=science+of+magnets&safe=high&cx=006665157904466893121:su_tzknyxug&cof=FORID:9#1742

I also found a related question that have some other interesting project ideas

My officemate & I were just talking over this.  The tricky part is "machine" - what can you do to make a machine?  Also, we're not sure what type (size, shape) of magnet you have available.
 
How about a little rocket launcher?  If you have disc-shaped magnets and if you put them end-to-end so that they repel each other, you can make a type of magnetic "spring".  Fashion a tube out of paper, making the inside diameter just a little bigger than the disc magnets diameter.  Then you can put the two magnets in the tube, N to N or S to S, so that they repel.  The trick is to keep the top magnet from flipping over, which it will try to do.
 
Stand this tube/magnet assembly vertically and drop a pencil (unsharpened is best) into it, and force the two magnets closer together by pressing down on the pencil.  Then let go!  The pencil should fly up into the air.
 
That's a pretty simple machine.