Cathy,
If you are close to average hieght and wiegt, you can easily go down to 1500 mg 2 x day. That 40000 mg was a result of the trials which were "over medicating" The manufacturer says that you should reduce the doseage 75% first time around and up to 50% if the symtoms are still dose limiting.
Here is a link that explains a lot of the dosage specifically on pages 30 to 32.
http://www.fda.gov/cder/foi/label/2003/208..._xeloda_lbl.pdf
Good luck,
Al