Simply place this 'gfx' folder in your main Counter-Strike 2D directory. It will replace your leet (t2) with the Condition Zero Leet.
If you want you can rename it to something else, here's a list:

ct1: Urban
ct2: Gsg9
ct3: Sas
ct4: Gign

t1: Phoenix Connection
t2: Leet (current)
t3: Arctic
t4: Guerilla