Go to www.half-life2.com , proceed to the media page, when it loads up hover your mouse pointer over the screenshots one of them will display a different picture when the mouse hovers over it (56k you have to wait a few seconds for it to happen), you will know it when you see it, click on it and you will be given a password screen, input the username "nova" and the password "prospekt", you will then see a black screen with a text box in it, now this should be a walk in the park for you slightly experienced people out there, so I'll leave it here for you guys to work your way inside.
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Ok so if you're a noob, what you should do at this point is bring up the page source code, you will see a lovely ASCII picture and below that a small web url missing its beginning. Now just put that onto the end of www.half-life2.com , and then you will see a picture of a HL beastie, put the name of that beastie into the the text box and voila a rather spiffy picture and the knowledge that they have done something over all this time, enjoy!