you should have a folder called "v4full" or "rustlerv4", place theat folder into your directory of ARMA 2 OA (it has the .exe's) then use a bypass such as yolohack at homescreen then join a game and press "home" and find startup.sqf in the rustler file that you put in the directory.
EDIT
for the yolohack to work you must right click, create new.... text document, place execVM "v4Full\startup.sqf"; into the txt and save as all files "startup.sqf". now instead of using the "start.sqf" as above you need to use your new "startup.sqf"