The password screen is the standard console, which can be gotten by holding Ctrl and Alt and pressing ~ (tilde). After the console's up, type "map game/mapname", replacing mapname with one of the codes listed below. For example, to start a new game in the Nexus Core area, you'd type: map game/core1.

airdefense1 -> Air Defense Base (beginning of game)
airdefense2 -> Air Defense Trenches
convoy2 -> Aqueducts
convoy2b -> Aqueducts Annex
convoy1 -> Canyon
network2 -> Data Networking Security
network1 -> Data Networking Terminal
process2 -> Data Processing Security
dispersal -> Dispersal Facility
process1 -> game/process1
hangar1 -> Hangar Perimeter
hangar2 -> Interior Hangar
mcc_landing -> MCC Landing Site
core1 -> Nexus Core
hub2 -> Nexus Hub
hub1 -> Nexus Hub Tunnels
mcc_1 -> Operation: Advantage
mcc_2 -> Operation: Last Hope
building_b -> Perimeter Defense Station
medlabs -> Strogg Medical Facilities
core2 -> The Nexus