Hi, my javascript knowledge is not great but i need to know if first it can be done and second how lol.

I have a table that is 100% in height but doesn't go to the very top or bottom of the page, its like a mid point. I have a table inside it that i want to move up and down when it is scrolled (abit like is done with the layers that i have seen) but i need to stop at the top of the table and again at the bottom so its refined in effect. does any1 know if this can be done and if so how

Thanks for you help

Adam