Word of Advice:
Spend the 100's of hours that you were going to spend writing code
doing more productive things, and buy a working package that will
have you up and billing ASAP. The increase in your collections, and
the saved time will probably pay for Emerald
(http://www.emerald.iea.com/) or Internet Back Office Billing
This is a biased view, since I have been there...
GreenSoft Solutions, Inc.