Question about server access and gateways
 

I have been setting up a Mandrake 10.0 server to run mainly a web server and ssh. I have set up the httpd server, and noticed that it will work (on the 'high' security setting, at least, but thats another story) when accessed from computers with the same default gateway as the server, but not from those on different gateways. I am not a total newb to linux, but am pretty close to it for these sorts of networking issues. Can anyone tell me what I need to look at to allow access from different gateways?