DNS setup in DMZ

[leungwai@Pacific.net]

hi, 
could anyone can help,
I have a DNS server in my netowrk DMZ, which DMZ was using 192.168.0.x IP
address (NAT), and each NAT address map with a real ip address by my ISP,
e.g. 192.168.0.1 as the GW, 192.168.0.2 map with real IP 202.85.21.133

The question is can I setup a DNS server under this situation ? I have
already register a domain with this real IP address, but I got confuse in
setting A and MX records, I need to use www.domain.com using 192.168.0.2 or
real IP 202.85.21.133 ? I found my DNS sometimes work but sometimes it won't
work. I've testing by Ping or dig from outside my network.

INTERNET
       |
       |
FIREWALL---------DMZ
       |
       |
   LAN



leungwai.