2002 transmitter programming

I recently bought a 2002 Aztek and when I got it there were no original keyless entry remotes, all they had were 2 of the 2 button your valet remotes. So I do not know if there is an after market alrm on it or not as the dealer did not know. They wanted a lot of money to purchase the transmitters from them so I bought one off of ebay. The numbers all match for my vehicle but I cannot get it to work. I have followed all the directions in the owner's manual and it still doesn't work. Can anyone help???