Just as a heads up, didn't see it posted elsewhere and I read the whole thread, you can get 'Conservationist' in the early chapter of Episode 1. I skipped HL2 when I got Orange Box because I played it on the Xbox when it first came out. I managed to get Conservationist as I was escaping the Citadel at the start.
At leat I think thats what I was doing. It's been a while. Just doing HL2 now, then omward to Ep1 and 2...