Converting between coordinates

This should possibly be in the developers forum, so I apologise if I’ve posted in the wrong place.

I have a large dataset of coordinates in EPSG:4326 and I want to convert them to EPSG:900913 (or 3857?). I’d like to do this conversion in Excel/OpenOffice because I need to do various different things with them. Can anybody point me in the direction of a formula that will do this? Also a reversal formula would be great.

The other option I have is to put them all into a PostGIS database in EPSG:4326, import that into a .shp file, convert that into EPSG:900913 and then export that back into PostGIS, then create a .csv from PostGIS and import that into OO. Not ideal!

Thanks for the help.

Have you already tried ??

It can deal with different projections and has interfaces do databases, if I am not wromg.