Ah, thank you very much, guys! I had no idea that UDK had it's own set of pre-created Material Functions. @LoTekK that would be great, thanks :) Tonight, I shall have a blast at combining the Multiply and Screen blend functions in UDK to achieve the Soft Light blend effect for some nice grunge.
I put together a package with a bunch of material functions that do quite a number of the blend modes a while ago. I'll have to hunt around for it; I'll put it up when I get a hold of it.