Oh, OK. Sounds like you need to configure the router to, well, not be a router - you need to be running it in "AP-only" mode (wireless access point + 4-port switch; routing functions disabled.)
Cup, several times now, wrote:
Unfortunately, setting up a Linksys router to operate in AP-only mode isn't all that intuitive...
First and foremost, reset the router back to stock configuration (see your user manual for how to do this.)
Log in to the Linksys (natch.)
Setup > basic setup.
-internet connection type: Automatic configuration DHCP
-network setup: local IP address to one on your subnet, but outside of your DHCP range (example: my Smoothwall's DHCP range is 192.168.0.100~199, my WRT54G is set to 192.168.0.254); subnet mask same as your network (default is 255.255.255.0); ignore gateway and local DNS (leave them blank.)
--DHCP type: DHCP server
--DHCP server: disable
Click Save Settings.
Setup > advanced routing.
-operating mode: router.
-Dynamic routing: interface: disable.
Congratulations! You've set up a Linksys wireless router to operate as an AP + switch only!
And, put a piece of tape over the Linksys' WAN port, so you're not tempted to use it.
That'll get you set up in AP-only mode, and should get you working correctly.