how do i know if i have anti-theft system in my 1999 mitsubishi galant

Usually, a light on the dash will indicate there is an anti theft.

I've never seen a light, but then again I have never had a button to push to find out. I guess I just dont want to short change myself and buy a 2 button remote when I could have a 3 button remote. Lets sappose I get a 3 button and hope I have ant-theft, if I don't, will i still be able to program it for the car? are the two different remotes inter-changeable?

Any Mitsubishi dealer can tell you if you give them your VIN#

I understand what you are saying. I believe the light would come on when you first turn the key on.