Win server 2003

I installed win 2003 sp2 on one of the drive in my PC. Active directory,DNS and DHCP installed as per the procedure. After installing it shows DNS forwarding IP address of my ISP DNS IP address.
My pc is connected to a wireless 4-port router/switch. Also after installing Active directory I couldn’t join one wirellesly connceted laptop in domain. It shows an error. Is it because my pc DNS shows ISP DNS ip address. I’m doing this for study purpose. Does anyone give me an idea what could be the problem.?