I actually have an Inspiron E1505 laptop and have had many keys pop off. It's actually quite easy to pop the key back on. You should only need to press it back on.
I have actually created a quick video of this in action for you...
You can see it here: http://dl.getdropbox.com/u/18982/INSPIRON%201505%20KeyBoard.WMV
Hope it helps!
~Jake