it's been done over and over and over and over and over. not to say you couldn't succeed, but you've got a lot of competition, and research to do:

http://www.livescribe.com/en-us/

http://www.irislink.com/c2-1626-189/IRISnotes-------The-Digi...

http://www.pegatech.com/

http://www.iogear.com/product/GPEN100C/

http://www.anoto.com/?id=19146

http://www.digitalfieldsolutions.com/

http://www.logipen.com/

http://www.paperiq.com/content/sections/dpfb.aspx

http://www.intellipen.co.za/

http://www.magicomm.co.uk/

http://www.amazon.com/Logitech-io-Personal-Digital-Pen/dp/B0...

http://www.destinyplc.com/flash/

http://www.mintgadgets.com/stationary-gadgets/pentel-airpen-...