This forum is not the game! You'd be suprised how many people come on here and then post in frustration as they can't work out how to play the game!

The game can be purchased from most stores as a DVD-ROM
OR
From the official online store: http://steampowered.com

From stores you can either buy CSS which will come with Halflife2 deathmatch and day of defeat source, or you can buy Halflife2 which will come with CSS, HL2 deathmatch, and HL2 lost coast.

From the official online store you can get it on it's own or in many different combinations with other games. Have a look, and if you have any other questions post back.

~ Alex