wireless issues

i have a wirleless router, wrt54g, that is also a 4port switch, running the ddwrt firmware. when im in one part of the room the laptops are fine in connecting, when i move it like 6ft further away they connect then suddenly lose conn, and take a min to reconn to the network, my desktops are not affected, just wireless devices, its like someone shut the wireless part of the router off and its rebooting that. but im sitting here and not had a problem but when i move to the couch it does it. and its not 6ft away, any ideas? it is a secured network, using a long wep key. plus i have mac address filtering to where only the specified mac addresses can get in. i know thats not fool proof but it has helped keep ppl off my network lol.