sql server 2000 not working properly in windows server 2003

i have installed windows 2003 in a server and installed a sql server 2000. i have some more pcs in network having windows XP sp1 but i m not able to connect to sql server 2000 through sql client Error message shows “sql server does not exists or access denied” i have installd sp3a(service pack 3) of sql server but still its not working can anyone help me?