Alternately, you could but a GPUSB from Shoestring Astronomy:
http://www.store.shoestringastronomy...roducts_gp.htm
I used one of these for about 12 months for guiding in conjunction with a webcam. The GPUSB connects from a laptop USB port to the 4pin ST4 guiding port on your mount. PHD then has a "GPUSB" option under the list of mounts.
They can also be purchased new from Bintel.
Ocassionally they are available 2nd hand for around $75.
Cheers,
Jeff