I really love that art, and the song while I'm at it. Keep up your amazing work as an artist, whatever you make!
In photoshop, the green was some slime texture overlayed over some green text and set to "overlay" layer style, with a little bit of Satin and Bevel&Emboss on the text layer's blending options.
The black is some nearly-transparent black brushwork with bevel&emboss and satin.
Be sure to play around with the Bevel&Emboss and Satin, as the default settings tend to look dreadful.
To access those things, right click on your layer and select "Blending Options".
Sorry I can't be more specific, I'm at work D:
Awesome cover art ^^