........It doesn't matter if people have your IP. Hell, simply by posting you've allowed the HLP admins to get it. They still needs to be able to: Port-scan you, Find a flaw in some software you're running, get past any firewalls you might be running, Exploit the flawed software and then do something meaningful against you.
And that's even if they give a ****.
If someone has enough skill to hack your computer knowing only your IP, chances are they're not going to have much trouble finding you behind a proxy.
And then we come to the matter of probability. There are hundreds of thousands of people out there playing MP games. There are hundreds of servers, each serving games for hundreds of people every day.
Now, say 1% of gameserver admins are capable and willing to hack you. This means you've got a 1% chance of encountering a problem. But then you factor in the probability that he's decided to go hack some people on that particular day and you're down to a 0.75% chance of being hacked.
Now, there'll be maybe 100 different people on this corrupt admins' server through the day, reducing your chances of being hacked to 0.0075%.
Then we've got to consider wether your computer is capable of being hacked. At a rough estimate, I'd say that reduces your chances to around 0.007%.
Now we account for the fact that people with enough ability to get you will be the type of people who only care about hacking you if you have something worth taking or destroying. Now, considering you're asking people to find an anonymous proxy for you because you are unable to find your own, this suggests to me you're hardly going to be some major software engineer working on the HL3 source-code and thus are barely worth the effort to hack. This does not reduce your chances of being hacked, but it means that if someone does get in, they'll probably get bored of your computer and not bother risking prison just to format all the worthless data on your hard-drive.
So, this brings the chances of you being hacked and attacked to about 0.00000007%.
This means that even if there are 10,000 non-admin hackers trawling the gameservers (which is probably a very low estimate) you've got a 0.0007% of being 'damaged' by a hacker.
In short, there's not much point in wasting your time trying to get games to work through proxies.
Besides, far as I know, games won't work through an anonymous proxy.