Hi,
I have internet connection by motorola router. My Xp pc get ip
by dhcp. Now i want to connect the astrisk server from my pc
for internet. Now it will be behind 2 nat 
Is there any possibility that astrisk will work ?
Please help .
Thanks.
Okay, Ensure following
Asterisk --> XP --> Router --> Internet
You have proper route setup on router for Asterisk.
You need to use externIP in the sip.conf as public IP on your Motorola router into asterisk so that it can do effective SIP NAT.
If still does not works, post the complete IP Addressing Scheme, I can try to workout for you.
VOIP behind XP does not work to well. I would try Internet -> Router -> Asterisk -> XP