- If you have Half-Life get this:
- Half-Life 1.1.1.0 full update

- If you have Half-Life ALSO get this:
- Counter-Strike 1.5 mod full download

- If you bought Counter-Strike retail off the shelf, get this:
- Counter-Strike 1.0.0.5 retail full update

A list of changes for Counter-Strike can be seen here, for Half-Life changes go here.