Any Wireless 'router' will do the trick, ignore the the modem thing, as long as it has a router in it it can rout all ur files around.
1)Plug it into the wall connect a computer/laptop with Ethernet cable (no need for cable after its setup)
2)Enter wireless router config page (it'll have a address like 192.168.0.1 or something depending on brand/model)
3)setup wirless network, put a password on
4)connect all computers/laptop(or w/e) to the wireless network
wala done, works the same as a wired network (besides wireless limitations of course)