Since you already got MS4W installed. The easiest way to publish a map service from Postgres is from MapServer which is component of the ms4w.
To start publish wms from MapServer,
1) Read thru the documentation of Mapfile which is the service definition file of how the WMS configured.
2) Read the ogr postgis connection documentation. You would be able to write the database connection follow the instruction pretty easily.
3) Once you got the valid Mapfile with correct postgis connection string info, you are able to publish the WMS for your topos.
MapServer is very powerful and easy to use. The file based service provide a lot of flexibility which is critical when you need publish something dynamically.
GeoServer is very popular too and has a gui which is extremely easy to use, by several click and your services are ready to go.
Other solutions are also available as well. But consider the community user base and tech support. I would recommend using MapServer or Geoserver for your case. We had our Mapserver holding USGS topo services as well, which is very stable,flexible and salable so just some FYI.
Hope it is helpful.