Uh, no. Abandonware usually doesn't become so until either the company goes under, or they stop selling it. Since HL2 is distributed mainly through a pay-to-download system, they probably will never stop selling it. So you're outta luck :P
You have to load all the crates in that level into the truck back there, but only after smashing them with the crowbar. Also, you must pick up each peice by hand, then place it in the truck. After that, GMan will drive up and offer you a ride to the biozeminades.
The piston things on Coast are called Poomers or Thumpers, and if you've seen\played Dune, they have almost the same function, except opposite. They basically keep the Antlions away, if you couldn't tell. ;)
The moving walls around C17 that almost kill you a few times are basically resource...
No, your CPU should be fine. I run HL2 at pretty much all high and 800x600, and get good framerates. I have an AMD AthlonXP 2500+, and also a gig of RAM.