If you meet the video card requirements and you use Steam, you can have either of those Half Life games registered to your Steam account in mere seconds.
Lost Coast is a standalone level given free via Steam to owners of Half Life 2, or owners of an NVIDIA or ATI graphics card. It was created originally as a tech demo of the Source engine to show what it is capable of. Deathmatch is exactly what it says on the tin. Half Life 2 as a PvP deathmatch game and a standalone product.
Because these are standalones, you don’t need to own Half Life 2 to play them. In addition, the large amount of computers using ATI or NVIDIA cards means that virtually everyone with a gaming computer qualifies for this.
If you are an NVIDIA user, you can also get an 11-level demo of the original Portal game as well as Peggle Extreme along with the Half Life 2 standalones.
Link for ATI users: http://steampowered.com/ati_offer1a/
Link for NVIDIA users: http://steampowered.com/nvidia/