how can i make server of open suse11 and how can i attach clients to that server with the help of dhcp.

Put the DVD in the drive, boot from it. Install Linux to your hard drive.

DHCP only gives out IP addresses, and needs a good bit of configuration information, before it'll work. Try Google for some DHCP how-to guides.

Any Linux system can serve as a "server." And that word, "server," can of course mean a great many things.

The specific role that you describe .. that of handing-out network addresses to DHCP-clients .. is a bit unusual. Most commonly, one of the routers (in each isolated network-segment) does that... and to avoid nasty conflicts, you must be sure that there's always only-one source.

To be "a server," a computer simply has to run some programs (they're called daemons in Linux/Unix and services in Windows) that are designed to "listen" on various TCP/IP ports and to respond in some useful way to requests that are sent to them that way. Computers usually employ a firewall to filter-out requests that should not be allowed to arrive.

A "dedicated server" is a machine that is, well, "dedicated to" the task of "being a server." Which means not only that it has a lot of hardware capacity, but that it isn't running many programs that are un-related to the services that it is intended to perform. Large-scale installations are usually "rack-mounted," so-called "blade" servers, where each computer sits on a single circuit-card and there might be dozens of them in a single case. Each of these machines is focused on a single task ... providing a single set of services very efficiently.

Yet... the software that runs on each one of them is "straight out of the box Linux." Many distribution-writers have found a good niche market of building pre-planned distributions that are targeted for this type of deployment, and they have built specialized (usually open-source) tools to allow you to manage "hundreds and hundreds of blades."