Root Name Server + TLD Server

Im doing an assignment for DNS on Ubuntu 10 using BIND9. Everything is on an internal network with private IP addresses and not access to the internet.
I have set up my own root name server (.) and a top level domain server (com). I also have another server configured for example.com. In the root name server's zone file I have the A record for the TLD server (com) and when I do "nslookup com" I get the address of the root name server and then the correct address of the com server. When I do "nslookup example.com" I get the output "server cant find example.com: NXDOMAIN".

What I want to do is when I do "nslookup example.com" I want it to return the IP address of the top level domain (com) server. I dont want to include the A record of example.com in the root zone file because then it will give me the address of example.com and not com. Can any please tell me how I can do this?

Here is the zone file of my root name server:
$TTL 604800
$ORIGIN .
@ IN SOA root.net. root.root.net. (
1 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
. IN NS root.net.
root.net. IN A 172.16.2.10
com. IN A 172.16.2.11

It's working how it should. In your config, example.com does not exist. So it returns NXDOMAIN. Tagged along with an NXDOMAIN response should normally be the root SOA record as well. I would also suggest using dig instead of nslookup. You'll probably be better off in interpreting and troubleshooting responses.