To run a map in SMOD, use the following command line, replacing "dm_underpass" with the name of any map you wish to run, and "skill 3" with your preferred skill, as above. It is not necessary to copy the map from the original installation directory. Using the following addcontents.txt file with the correct edits (see enclosed readme) will allow you to run maps from any directory. With one installation you can run maps from regular HL2, HL2DM, CS:S and from SMOD.
You can also play maps from other mods from within SMOD. This is done by mounting the resources for those mods using the addcontents.txt file, as described in the download below. The mod can then be started using the console or the command line below, substituting dm_underpass for the first map in the mod.
"C:\Program Files\Steam\Steam.exe" -applaunch 220 -game "c:\program files\steam\SteamApps\SourceMods\smod" +map dm_underpass +skill 3