Check out Johnathan Williamson's tutorial on using alpha maps to create textures during sculpt mode in Blender 2.5.  Though Blender is no Z-Brush, it is still capable of doing some really awesome stuff.  Follow Johnathan's easy to follow tutorial.  Even if you're new to Blender, you won't get lost in this one.  Don't forget to check out the other videos that show more about the Blender 2.5 at www.blendercookie.com .