IS there Linux server internet gate way like ISA?????
 

My company 're using ISA for Web and proxy server?? But if not use this is there any software in Linux like as it. with same function...

you want to use linux as a routing gateway? that's a doddle... ;) for plain gateway functionality you'd do it using ip masquarading - check the howto at http://tldp.org and for proxy work, that would be done with "squid". if you're all new to this you might want to try a firewall application such as firestarter, which includes all the ip masq stuff as well.