sims 2 pets installation help?

alright so i installed the sims 2 pets on one of my computers, then had to uninstall and move it to my other computer because the virtual memory was too low. sims 2 is alrady installed on the computer i'm trying to move it to and everything, but you know that code you have to type in for it to begin installing? yeah, there's my problem. i have no idea where it's supposed to be, because i can't find it. i know i've used it before because it was installed on my other computer, but now it's not on the back of the booklet or case or anything! might sound completely stupid, but where in heck is it??
and is there any way i can install without the code, or get another code?

please help.