Make that map
Find a relevant WMS layer. This is harder than it sounds, as they come and go quickly. http://www.lib.ncsu.edu/gis/ogcwms.html has a nice listing of sites that list them. A good site ishttp://126.96.36.199/ArcGIS/services/FWS_Wetlands_WMS/mapserver/wmsserver?– try the XXX layer. Here I usedhttp://giswebservices.massgis.state.ma.us/geoserver/wms?, which I got to via the NCSU site above, then their directions for Geodata.gov. A nice feature of the Geodata.gov site is that from the service availability option they check whether or not the WMS is live and valid.
Add the layer, then pick the Schema and Add to Map (I used the 2008 color orthos 30 cm layer from 2009 – its about 1/3 of the way down the list, and is not statewide coverage). It takes a minute, but imagine downloading and managing all of the tiles that go into the WMS!
Save, and use it again another day
The white bounding box is part of the WMS layer. You can go into the Style Editor for the WMS layer, select Transparency, then pick the white background area to make it the transparent color.
Have your own imagery that you want to make available as a WMS layer? Map Server can do that - more on that later.