We haven't tried this in MapPoint 2000, but mapping records using six-digit OS Grid references appears to work fine in MapPoint 2002. You need to combine the easting and northing into one data field separated by a space (comma doesn't work). All the references we tried produced matches. The OS Grid reference of "430800 386400" produced a pushpin a few miles west of Sheffield city centre, and "470800 171700" showed up just south-west of Reading. These locations seem to be the same as those generated online using the Get-A-Map service on http://www.ordnancesurvey.co.uk/.