Client can’t Ping DC in windows2003Doma

I setup a new Windows2003 DC domain ,and add about 20 WindowXP client to the domain , I am very confuse to find DC server can’t ping a lot of Client , but all the client can Ping the DC , I check and disable the Firwall on both of Window2003 server and XP client. what surprise is DC server can ping some XP which runing windowXP SP1 , I install DHCP ,DNS on same one DC , TCPIP setting in server :IP 10.35.122.11 Mask 255.255.255.0,Gatway: 10.35.122.1 . DNS server and DHCP server is 10.35.122.11. any prompt help will be highly appreciated ! !!! thanks very much in Advance !

Victor