the alarm system on the 00 - 04 cars is weird.
usually turning the key on / off 3 times will turn the alarm off.
at this point you should be able to start the car.
but if the alt died, and the battery is dead,
once you disconnect from the ''jumper'' car battery, the engine will die.
with a decent battery you can drive it until you use all of that electricity.
so to review,
connect the jumper cables,
on / off 3 times,
then start the car.
PS: any alarm remote that looks like the one for your year should work.
alarm info : Subaru Keyless Entry, Security Alarm, Immobilizer Key, Remote Start Systems. Most years and models