Rhel5.0 firewall server for my network

[aamdevan]

hi i am new in linux..i have to configure a firewall server for my office.we r using RHEL5.0,we have public ip for web server and mail server..thats ip also use to connect client system for internet access
Pl see my network arch
--------------------
firewall server |
ext network |
eth1:61.247.253.235|
--------------------
int network |
eth0:192.168.1.1 |
--------------------

|---->web server 192.168.1.2
|
firewall
server------->mail server 192.168.1.3 (optional)
|
|
|--->Clients for access internet(192.168.1.X)

Here my requirement,
1.Web and mail server should be bublished
2.client can access internet
3.all ports should be closed,when ping in firewall server from outside network.
4.all ports should be closed,when ping in firewall server from inside of network(internet access client) except what i mention particular ip,

now,what should i do?..please help me any body step by step
thanks
aamdevan (aamdevan@gmail.com)

[svar]

you can use firewalls like csf or nsf all block all the ports, configure the firewall according to your requirement. i have heard it but i have not implemented it.