You cannot buy a replacement chip for 96+ BMWs... There are two options.
1. Remove the computer and send it away to get reprogrammed, the car will be undriveable until the computer is reinstalled $399
2. Buy the programmer, plug it in and push the button to reprogram the chip $399.
http://www.activeautowerke.com/softw...i-software.asp
http://www.dinanbmw.com/html/325-e46/e46-325_soft.htm
http://www.bimmerforums.com