Although I am not familiar with the devices in use, I would make an assumption that the NAT functionality of one of the firewalls is causing the problem you’re having. You would want to turn this functionality off on both devices if and only if you are not connecting to the Internet. Another option is to connect the devices together on their LAN side and have each of them use a different IP address, and turn off DHCP on one of them, if they are supplying it. This will eliminate the need for turning off the NAT and probably let you have better performance overall.
The netgear router probably doesn’t have a route pointing back to the NetScreen firewall. Also check the NetScreen policy to make sure ICMP is allowed from your trust side to the NetGear side.