...well i recommend you use
-Milkshape (for add-ons vehicles - basic models etc etc)
-Mission Editor (Its for maps)
-Some Sort Of Scripting Software For .cs Files (i use macromedia dreamweaver)
-Skillz
do you have any of these? if not, go get them. you will definately need them.
and look up on the forums about them. i cant be bothered to tell you how to work them.
duck