Yep, there are several tutorials and mini tuts around. Ascension just posted a pretty nice one up just a few days ago for making trees in PS that you should be able to adapt. Also, DanChops took a modified method from Robs tutorial and made a little mini tut in a post around 4 weeks ago.PS: Are there any good tutorials for making forests in GIMP?
Also, watch out when using drop shadows as they tend to make things look like they are floating above the ground.