do a google image search for a 'grunge texture' or 'grunge background'. Find a good size pic or one, put it in its own layer above the type.
Make a selection of the text layer (so all the text is outlined), then click the little button "Add layer mask" in the bottom of the layers palette. The grunge layer should now be cut so only the text shows.
Turn the opacity down to reveal your text underneath or play with different blending options for cool effects. Good luck.
"The game is to be sold, not to be told"