To install:
Place the usermaps folder in your Activision\CoDWaW folder,

(I.E. C:\Users\Username\Local Settings\Application Data\Activision\CoDWaW

or in my case (Vista) C:\Users\Username\AppData\Local\Activision\CoDWaW)

and place the mods folder in  the \Activision\CoDWaW\
(Replace if you have to)

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To use:
Start your version of Call of Duty: World at War, then choose mods --> mp_CoDJumper

and start a server either by the Create a Server function or bringing down the console

and entering either "map mp_gap" or "devmap mp_gap" (without the "")

Make sure:
You have both the latest version of the mp_CoDJumper mod and that you are using the gametype "free-for-all"