Server 2003 Problem

I me have some experience with networks, however I have no expericence with servers. To solve this problem I set a lab network at my house and I have a 3 boes on it. One is running Red Hat 9.0, anouther is running Windows XP Pro. and my server is running Server 2003. the Linux box is runnign a filesharing server and a http server and is on a workgroup with the XP box, however I can not get this work group to join the domain can someone give me some possible problems or soultions.