slow nslookup for external domains

[tom at hottestnet.com]

I have a problem for DNS query. If I used my own DNS erver, it took
long time (4.8) to get the result:

bash-2.05# /bin/time nslookup 203.202.1.1
Server:  test.mydoamin.com
Address:  192.168.3.2
*** test.mydoammin.com can't find 203.202.1.1: Non-existent host/domain

real        4.8
user        0.0
sys         0.0

But if I use external DNS server, and do the samething, it's faster:
bash-2.05# /bin/time nslookup 203.202.1.1
Server:  vnsc-bak.sys.gtei.net
Address:  4.2.2.2

*** vnsc-bak.sys.gtei.net can't find 203.202.1.1: Non-existent
host/domain

real        0.0
user        0.0
sys         0.0

My DNS server version is 8.3.3:

bash-2.05# /usr/sbin/in.named -v
in.named BIND 8.3.3 Wed Feb 18 23:46:02 PST 2004
        Generic Patch-5.9-May 2002


Any idea, why? Thanks.