I got a Portal gun working in Half Life2. This is how I did it:
Step 1 - Copy the HL2 maps into the Portal Dir.
Step 2 - Open Portal
Step 3 - Go into Dev. Console and open up one of the maps.
Step4 - Go back into Dev console once map is loaded and type SV_Cheats 1
Step 5 - Type impulse 101
Step 6 - Type upgrade_portalgun
Step 7 - And then there will be Cake LOL
I can't figure out how to get the sound working though, if anyone can help me figure this out it would be greatly appreciated