I was playing around tonight with cs5 photoshop and it has a 3d feature. You can basically create a 3d shape from a custom shape by adding the "reprosee" feature in Photoshop under 3d...I'm sure I butchered the spelling...I enclosed a picture of something I did very quick. It will export as a obj which can then be converted to a stl. It also had a depth map feature but it didn't look like a good quality for carving...who knows maybe someone wants to play with it and figure it out. I exported the obj to 3ds max and it came into max fine..looked blocky though but I suppose you could add a mesh smooth modifer and it would be ok..didn't try.
Looks very limited in terms of 3d but if you some basic shapes in a 2d drawing program this might be the ticket...It runs slow...I am using a dell m90 with, duo core 2.2, 6gb ram and a nvidia fx1500...and still slow..#ds max runs like a clock cept for some of the rendering so who knows. digital tutors had very neat tutorial on it...cant repost the tutorial as it's a paid to learn type site.
Anyways maybe someone can look at it further and maybe it will help.