You have a couple options. You can download it from Steam online for about $20 I think to play on your PC. Or you could find someone who owns the Orange Box for the PC and could loan it to you. I own it, but for the Xbox 360 and so you could only play it if you came over and played through the whole game over the course of about 3 hours, which people have done, but you would probably prefer to play it at your leisure.

I think Alec owns it for the PC. I'll bug him about it at Video Game Club to see if he can part with it for a day or two.