Just quickly (sorry I have to be out soon);
Reliability is referring to how well you measured things out and the accuracy to which you measured them (also the accuracy on the instruments themselves), if someone else were to follow your method would they get the exact same results etc.
Validity is how well your experiment tests the hypothesis.
Hope this helps, if not, post and I will try to clarify in more depth for you, or I'm sure someone else will also try to help you out.