These are standalone .exe installs which require no crack, no key, and no steam account. Just install and play. Opposing forces and Blue Shift are expansions, you need Half Life Installed first before installing them and playing them.
The "Hi Def" pack is included in the install options. I dont know why it's called that but this game looks better with it, here is a comparison screenshot:
After/Before
http://www.megaupload.com/?d=U5CIMSKG -part 1
http://www.megaupload.com/?d=UMLPIXJM - part 2