I have never used a digitizing probe before. Has anyone used this probe?
http://cgi.ebay.com/CNC-3D-Digitizing-Probe-Mach3-stepper-motor-routers-/330376888595?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item4cebff4113

I bought one of the ones in the link below and it worked well for me, it appears to me to be more accurate than the one you mentioned.  There is also a long thread about it in the "bargain basement" section in the forum here.

http://www.wildhorse-innovations.com/index.php?_a=viewProd&productId=80

Paul T.

Thanks, I may give that one a try.