| >> Now should i install windows server on the mainframe computer <<|
The simple answer is you don’t. A mainframe computer is usually a huge thing that has a room all to itself with it own air conditioning and a team of operators to control it. It usually comes with a proprietary operating system supplied by the manufactures like IBM. You would not want one in your home unless you live in a mansion.
I think you need to do a bit of reading and start of the simpler things like peer to peer networking. Windows XP isn't going be enough to set up a server. All Windows XP Professional can do is act as a client to Windows 2003/2008 server or as another computer in a peer to peer network.