Hey dave, take a look at this page for starters: http://www.mathsisfun.com/pythagoras.html

There is a pretty simple activity about half way down the page using paper and scissors.

Using real life examples or actually physically acting them out (using different length ladders; creating triangles outside on the oval - use string and measure the lengths; etc) may also be another idea.

Hope the ideas on those pages are useful. Have fun.