http://www.primotechnology.com/2007/10/17/half-life-2-portal/

Here's the brief instructions on how to enjoy the Portal gun in other Source games!  Games you obviously own if you already own Portal!

• First off, backup up your entire Portal directory in a safe place. It’s the folder marked ‘portal’ in ..Steamsteamapps(your_username). We, nor Valve, take any responsibility in the unlikely event of you hosing your game files. Worse comes to worse though, you could always just redownload.
• Next, download and install, if you haven’t already, GCFScape. This handy program will allow you to access the cached game files for any Source-powered game, in addition to several other Steam games you may have downloaded.
• Once that’s done, browse to the directory ..Steamsteamapps. There, you’ll see all the available GCF archives. We’ll start with Half-Life 2.
• Open the GCF marked ‘half-life 2 content.gcf’ You’ll see a directory tree in the left pane. Click the box to the left of the folder marked ‘hl2’ to see the directory listing contained within it. Then, right-click ‘maps,’ select ‘Extract’ and extract the entire folder into the directory Steamsteamappsthe_great_bundiniportalportal. This will merge it with the existing Portal map folder.
• Do the same with the ’scenes’ folder
• Fire up Steam and run Portal. When it’s done doing its thing, open up the developer console with ‘~’ (you may need to enable it under your keyboard options).
• At the console, type ‘maps *’ to list all the available maps. Now that you’ve imported the Half-Life 2 maps, this will be a fairly lengthy list and some of the names, like citadel and canals, should seem familiar.
• Type ‘map’ and then the map name to open that map. For instance, ‘map d1_canals_01’
• When the map is done loading, pull up the console again and enable cheats by entering ‘sv_cheats 1’
• To give yourself all weapons, including the portal gun, enter ‘impulse 101’
• Depending on how far you got in Portal, you may need to upgrade the portal gun to fire both portals. Enter ‘upgrade_portalgun’ to do so
• Go lay waste to some alien scum with the power of portals!

Sweet, thanks Ben!

For the first time in a VERY long time, I feel an intense urge to play a PC game...

SWEEET!!!!!!!!

I've never even heard of that gun, either I'm not far enough in HL2 or I'm not playing deathmatch enough.

/facepalm. It's from Portal, the new game included in The Orange Box.

@cool48:

 It's not in the game proper originally.
 

OMG thank you so much Ben! I'm going to try this right away.

Also, TF2 t-shirts for sale!

http://store.valvesoftware.com

I like the style of the Soldier shirt...I'm gonna wait to see what the Engineer shirt looks like though.

I think I'm gonna get the Portal shirt soon though...I've put it off long enough...I already have the "Evolution" shirt...thought that was freakin sweet.

I really hope they come out with a way to use it on the consoles. I'd love to try this, I've been thinking about the whole time I play Orange box.