I've posted about this process before, the piece was done with Alchemy 7.0 and finished with a touch of color and texture in Adobe Photoshop
Above is the initial alchemy sketch for some sort of mech
Above is the initial alchemy sketch for some sort of mech
and here it is after some work in Corel Painter Essential 2.0, I actually think the original sketch is more powerful though. Get Alchemy Alpha 7.0 here, it's free and open source, so you have no excuses.