Sorry if it's repetitive, but...
http://www.silverblades-suitcase.com/tutorials/htm/22.html

have a read, and on my pther tutorials, ESPECIALLY the one on DIRT MAPPING, and go get my free dirt map material, it really does help a huge amount :)
http://www.silverblades-suitcase.com/vue_mats/dirt_mat.zip

As peggy said, Lighting is crucial

here, lighitng is defailt

Here, lighting is soft and render settings tweaked

And on this pic

http://www.renderosity.com/mod/gallery/index.php?image_id=1642282

note how dirt effects applied with Vue procedurals mixed with image textures, gives a MUCH better effect than if they had been un-stained.

:)

"I'd rather be a Fool who believes in Dragons, Than a King who believes in Nothing!" www.silverblades-suitcase.com
Free tutorials, Vue & Bryce materials, Bryce Skies, models, D&D items, stories.
Tutorials on Poser imports to Vue/Bryce, Postwork, Vue rendering/lighting, etc etc!