chipping my ecu????

i was wondering if anyone out there ever chipped their ecu's? and if they had what companys are good ones?does this really add hp and tune my cAR? INTRESTED IN BUYING ONE OFF E-BAY ???THANKZ

Oh Ya And My Car Is A 91 Crx With A D15b6 Si Withb The Pm6 Ecu.

I can chip them, $100