what is the activation code for the sims 2?

Answer 1

You find it on the case in the older games packaging pre2006 - on the back of the CD case at the bottom. They've repackaged the game this year so the required code is now on the manual that comes with the game and is printed at the top on the back.

Another way to get the numbers:
http://www.modthesims2.com/showthread.php?t=176239

Here's the official help file regarding registrations and key codes:
http://support.ea.com/cgi-bin/ea.cfg/php/enduser/std_adp.php?p_faqid=7805&p_created=1094762905&p_sid=Rz2ez3gi&p_lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J0PSZwX3Jvd19jbnQ9NSZwX3Byb2RzPTcsNzAwJnBfY2F0cz01NjYsNzMwJnBfcHY9Mi43MDAmcF9jdj0yLjczMCZwX3BhZ2U9MQ**&p_li=&p_topview=1