How to connect a server-client network using XP SP3

You can't, XP can't be run as a server. You are missing a lot of needed info in your post. Such as area they are in, current wiring, connection type needs (wifi for example), file storage, number of users, type of business, etc...
Do a bit of research on networking first online (web search will get you hundreds of sources) then if you have issues with something, come back to your post and fill in the details.