Quick Tip in photoshop CS2

can someone show me how to create a mask that will onlty reveal the image below it?

i have tried looking online for this tutorial and have come up empty handed.

what i would like to do is type some text on one layer, then on the layer underneath have a picture. then mask it so only the portions of the picture that are shown are in the shapes of the text.

i know it should be a faily simple process, but i cannot figure it out.

thank you!!

-jason