Hi, are you sure that it's a client computer that has the same IP, since it's a HSRP DUPADDR's message my guess is that you have another router/switch running HSRP with a missconfigured interface.
But then again, I could be wrong.
Like the previous post says, using a DHCP is recomended to build away problems like this.
Here's an explanation off this error message from the Cisco website.
Explanation
The IP address in an HSRP message that was received on the specified interface is the same as the IP address of the router. Another router might be configured with the same IP address. The most likely cause of this condition is a network loop or a misconfigured switch that is causing the router to see its own HSRP hello messages.
Recommended Action
Check the configurations on all the HSRP routers to ensure that the interface IP addresses are unique. Make sure that no network loops exist. If port channels are configured, check that the switch is correctly configured for port channels. Enter the standby use-bia command so that the error message displays the interface MAC address of the sending router, which can be used to determine if the error message is caused by a misconfigured router or a network loop.
