I was wondering if there is a way that you can scan through a firewall and see the servers open ports behind the firewall if this info helps i trying to scan througha netscreen 5xp hardware firewall

Depends on how the firewall responds to open and closed ports as well as how it handles different flags in the packet.. Try nmap and some of the optional scan types, like Ack, fin, blah,blah,blah

Also lookup information on firewalker or hping2 which allows you to probe internal devices. I will look for the texts I used to learn with

if the telnetport is open on the netscreen (port 23).
the defualt password is
user netscreen
pass netscreen
(you may have to go up a ip or two)

then you can have READ ONLY aCCESS to the console and can ping internal subnets and use other built in tools

hping2 is really, really, cool. It will let you listen to broadcast on one machine and spoof ICMPs from that machine to another one and such. ICMP is a unique protocol and hping2 really shines in exploiting it.