Was playing CS:S the other day after being bored for a while, and came across an interesting mod on a CS:S server.
They had people spawning with a weapon based on what level they were currently at, to move on to the next level, they had to make a kill with the assigned weapon.
The mod started people out with a pistol, and worked it's way up trough SMGs and then rifles, and finally came to the last 2 weapons, at level 23 and 24 respectively, that is, a kill with a grenade and a kill with a knife, which is really hard to do considering you only have a nade or a knife at spawn while everyone else has a gun of some kind.
If by any chance you make the first kill with the knife, you win the map.
The official gun game mod is located @
http://www.cagemonkey.org/joomla/
I don't know if it's possible to port or even clone the mod for CS/CZero but it'd be a nice mod to run.
lailoken