Valve requires a steam account for Half-Life, Counter Strikes and such. To get an account...legally.. you have to have a new copy of the game.
Before I bought Half-Life II, I bought my vid card which came with CS Condition Zero. Just to get a code key to play I had to ask for permission, meaning connecting to a site. After that they sent my a key to play the game.
As soon as I loaded Half-LifeII with CS Source, my CS Con Zero merged with the Valve Steam account.
All of my games are legal and I have no problems.
Hope that helps.
Your Hardware Guide.