Finally! In addition to reprojecting from 4325 to 900913 in GeoServer, I also had to declare the projection as 900913 in the layer properties, like so:
var wms = new OpenLayers.Layer.WMS('Rezoning Scenario',
'http://localhost:8080/geoserver/envision/wms',
{'layers': 'envision:basecamp_property'},
{isBaseLayer: false,
projection: 'EPSG:900913'} //This part was required!
);
map.addLayer(wms);
For some reason, not many examples I've found have had to do this, but I did to make it work.
R