It is not possible to spawn a portal gun in half life 2, but the opposite is INDEED possible. Portal uses the orange box version of source, and so for reasons only known to valve, portal was shipped with all the hl2 guns still coded in, complete with models, materials and sounds. therefore, if you use a tool called GCFscrape (google it) you can open up the hl2 content gcf (found inside your steam directory) and copy all the maps and materials into the portal folder. This means that if you open the console, you can type map D1_trainstation_01 to go to the beginning of hl2. This works because all of the npcs are still scripted into the version used in poral, and that e sripted events are inside the .bsp's (map files) This also means you can spawn zombies in portal, and pitch the combine against glad0s (not as interesting as that sounds, but just as funny) also on a side note, the hl2 map are not made to be used with a high tech marvel of modern science, so you can create portals everywhere except displacements (rough terrain) Npcs also do not react very much to portals, and their AI can get confused easily.