.MAP files cannot be viewed with DarkBASIC directly. There are two methods to view the map.
1. Compile the map file into a .BSP file and use the LOAD BSP command. For further information on editing and compiling .MAP files, please look at the Valve Hammer Editor and Zoner's BSP build tools at
http://collective.valve-erc.com/index.php?go=hammer or GTK Radiant editor at
http://www.qeradiant.com/?data=files&files_dir=1
2. You can use my .MAP to .CSM Cartography Shop map file converter on my site in the tools section. This will convert .MAP files to (V3) Cartography Shop map files. If you have Cartography Shop, you'll need the Prefab Maker which can be found on the TGC World Building/Cartography Shop/Downloads/Misc section.
Paul.

Home of the Cartography Shop - DarkBASIC Professional map importer