Help me to use ASM400 behind NAT

Does anybody know how to use Tenor ASM400 behint NAT router?
I want to use ASM400 in my private network and I use a windows 2000 system as a NAT router but the ASM400 dosent work in my private network and can’t register with other gateways over the internet.
I have turned off the NAT for H323 protpcol as the Quintum says in thair documents and also added my windows 2000 public address in ASM400 as externat NAT IP but the unit dosent work yet.