In reply to Sam.

Sam, I am not aware of Google Map API directly using easting and northing coordinatates. At this point, your best bet would to convert easting and northing into latitude & longitude using one of the tools available, e.g. http://www.ordnancesurvey.co.uk/gps/transformation (single transformation), or http://www.ordnancesurvey.co.uk/gps/transformation/batch (batch transformation). If Google appends its API to handle easting and northing directly I would like to hear about it.