go Start then Run in XP - (Windows key plus R in Vista and Windows 7), then type in the following, including all the spaces:- cmd /k ipconfig /all -- then press Enter and from the black form that shows up, take a note of the numeric code beside the word "gateway" -- usually something like 192.168.0.1. Type exit to close the black form.
log into the Linksys
setup your wireless security
disable DHCP and change the LAN IP to match the Gateway IP you looked up but ending in 253 instate of 1.
connect one of the four LAN ports of the Linksys to the main router.