Hi,
We are doing this very thing for several of our projects.
As Mitch has said above, you install ODK Aggregate on a postgres+PostGIS
database. Using Geoserver's SQL Viewshttp://docs.geoserver.org/stable/en/user/data/database/sqlview.html,
we serve out the required data as a WMS service.
We consume this WMS service in out OpenLayers based WebGIS