To add a tiled basemap to a gmap created with views (and the gmaps) module:
1. First make sure that you have a gmap set up through views. This is a good tutorial: http://groups.drupal.org/node/19614
2. Next download the GMap Addons module, if you haven’t already done so
3. Create a map tile structure using something like tilecache, mapcruncher, or ArcGIS (you can generate a map with the google maps scheme, just not sure where to get an xml that would adequately describe the scheme to ArcGIS)
4. Finally add a tile overlay macro within the style (GMap) configuration for this view. Use the following form:
… notice you don’t need to substitute anything for Z, X, or Y … these correspond to folder numbering as generated with tilecache (or other tiling program) using the google maps scheme.
If you save the view you should now be able to see your basemap in a page generated by that view.