Certain Area Transparency on Banners for PS7

Okay, here is my issue. :D

And yes, I've looked through the memories.

I've got a banner I'm working on, and I want to make the edge transparent (it's for a layout), so that the background will show through in that part instead of the banner's corner being there...yes.

How do I go about making something like that transparent? I don't mean with checker-background, but full-blown just-plain-not-there.

I use Photoshop 7. :)