I have used an extender (unpowered) using CAT5e cable and it works over 40 metres.
http://www.maplin.co.uk/Module.aspx?...ender&doy=29m3
You can get active extenders from Maplin to take the signal further than the standard 5M without it needing to be powered.
http://www.maplin.co.uk/module.aspx?...97272&doy=29m3