IP address different between internal and external pinging

So our company network receives a completely different IP address when pinging or nslookup a domain, compared to to doing a traceroute from network-tools.com, or any other external ip\whois lookup site. the ip address that's listed on the external lookup sites is correct. i've tried using different computers from the network(both XP and windows 7), flushing the DNS cache, and still get the same results. i followed the instructions from these threads:

http://support.microsoft.com/default.aspx?scid=kb;en-us;320760

http://stackoverflow.com/questions/666510/under-what-conditions-with-nslookup-and-ping-return-different-ip-addresses-on-wi

nd still cannot resolve the same, correct ip address. Thanks in advance!