It's alot easier than you think man.
First of all.. make sure your layer is white.. and your colours B/W.
Go to Filter>Render>Clouds. (This is optional I guess.. but it seems to work well for me).
Make a new layer.. and add a grunge brush somewhere.. still in black.
Make a new layer.. and add another grunge brush somewhere.
Keep doing this until theres loadsa layers and so loadsa bits of grunge.
Combine it all.. and go to Image>Adjustments>Hue/Saturation.
Click 'Colourize'. and then just fuck around with the bars.
I always keep pressing undo after seeing the colour version and add/remove brushes etc..
It's that easy.
Of course you can do it in colour brushes/clouds for added effects.. but thats the simple way.
I'm still waiting for you hoes to start tutorials too.