Trevor, good effort for you first go of HDR. Like Nik says, use PhotoMatix or Dynamic Photo (buggered if I can remember which was the free one to try (link incorporated... LOL))
With the HDR, you should find more definition in the trees and shadows etc. Hope this is of some help.
Mark
PS: I know that subject quite well. HAve passed it on many occasions. Wonder why I've never stopped to photograph it though!!!! LOL
