join xp workstation to server 2003 machine.

I have been trying to create a domain for my friends business using 2003 server, and I have created all of the computer and user accounts in AD but I cant join any xp workstations to the domain. I can ping the workstations from the server but cant ping the server from the workstations. I believe all of the physical connections are correct (server & WS’s connect to a switch)is there some sort of security function on the server I don’t know about? when I try to join the domain, it gives me a Dns name doesn’t exist type error. with a network of only 5 WS’s do I really need to run DNS /DHCP on my server as well or use the ISP’s servers for this? PLEASE HELP!!!!!