linksys wrt 54gl as router and range extender. perfectly suitable for smaller companies because of their os interchangability. (
http://openwrt.org/ http://www.dd-wrt.com/site/index there are some more but you can get a good over view on this based on the given information).
it can nearly do the stuff as a high class cisco router.
you could even use the linksys as dongle - just plug a normal network cable in your pc and in your router - config the router to connect to the wlan network (with dhcp ip) with the main router and let the main router be a dhcp server too.and you could