installing headshot script

Unzip "headshot.cfg" to you half-lifecstrike dir.

                        executing headshot script

Just Type "exec headshot.cfg" in console (hit ~ to get there ;).
The program will tell you how to use the script, etc. after execution.

                        special features in headshot script

Well 1st of all, and most important is that this headshot script doesn't lock your mouse.  Also the headshot script is automatically disabled when you duck (bound to CTRL) and when you hit 4 or 5 (4 = Grenades, 5 = Bomb for Terrorist).  Also, one bug is when you're above the person (like if yer on one of the roofs in assault and your target is on the ground) you will shoot OVER their head, you might want to hit "f10" and disable the headshot and after you're done shooting at that target hit "f10" again to enable the headshot.