In addition, you mentioned you're running Windows XP, which does not come with a DHCP server, so I'll have to assume the DHCP client on your Windows XP machine is not responding or working correctly.
While it would be useful if you could provide some more information about the problem and also let me know if the system's event log is reporting any errors, there are a few actions you can take to try and resolve the problem.
First, if you enter your administrative tools located in the Control Panel, you can launch the Services console and check to see if the DHCP client service is enabled or not. This must be enabled in order for your workstation to obtain an IP address offered by a DHCP server nearby.
Secondly, check your event viewer for any system logs that might provide a hint or two as to what the problem is. With that information, you can visit Microsoft's support page for more information on how to resolve it.
Finally, check you don't have a firewall enabled and that your network card drivers are properly installed.
With all the above, you're surely to find the source of your problem and resolve it.
Best of luck!