Good attempt here, although it seems a little dark, i.e. there does not appear to be much in the way of stars, is this due to the cloud? The trouble with one single exposure is the noise that becomes apparent thus limiting you on how much you can push the exposure in PS. What ISO did you have the camera at?
In the past I have gone upto 800, but I use a different technique where I let the camera take 100 or so 30sec exposures one after the other.
Try reading these threads that I have posted on my technique
Star Trails Take 2
Star Trails Take 3
I have been meaning to write a guide on this, as promised to Gordon. I will try and do this after my exams on the 12th Jan. In the mean time, if you need anything else clarifying feel free to let me know.