Can you please provide some details about your new computer? Do you really need an expander for your home network? Your wirless expander works wirelessly the same way a hub or a repeater would. It receives a valid WiFi signal and rebroadcasts it out effectly increasing the range of your wireless network. Is your new computer a laptop or a desktop? Does it currently support wireless?
Assuming your WiFi router is set using standard settings it should provide a wirelessly enabled computer to receive IP addresses via DHCP. There really shouldn't be an IP conflict unless you have your computers IP address hard set to the same address that something else on your network has.
Please provide some additional detail.
Thanks
Jeff