Portal is not currently available on any emulated systems.
There is no emulator for the Xbox.
emulator-zone.com
Get Your Emulator From Emulator Zone (nullDC) Games dcisozone BIOS Emuparadise
You need to get a emulator to play them. Go to the emulator zone to download a emulator. Remember to get a emulator that can run your type of game.
emulator-zone.com
Dolphin emulator
If you are playing this on No$gba emulator, click "A" about 100 times when Cyrus is opening the portal. The people who made this ROM forgot to add this scene. The emulator doesn't actually freeze, it is still running. This is not fake. It really does work, I did it 20mins ago! Happy gaming if you read this!
There is no 3DS emulator, not yet.
emulator-zone.com visualboyadvance is the best.
The best emulator is NO$GBA
Dolphin - emulator - was created in 2003.
Hercules - emulator - was created in 1999.