Adding a kill counter

[OptimusRhyme]

Hello all, I am currently fixing up an old level I have and one option involves an endless amount of enemies as a sort of "survival mode".
To make it more interesting and challenging, I plan on adding a kill counter on the screen. But I need some help with the mechanics.
How do I add the counter to the hud? And what output do I put on the enemies? I don't have experience altering the hud at all.
Thanks for the help,

 

[tschumann]

For modifying the HUD, I"d look here: http://developer.valvesoftware.com/wiki/Category:Programming (User interface (VGUI)).
What do you mean by output on the enemies? Are you looking for a way to count the kills?