I recommend using a better client adapter. I'm not sure this will significantly help you out, but I know the ORiNOCO cards are by far the best you can buy and should definitely increase your speed. Also, search the forums for the increased power tweak for the WAP11 which will help your coverage. I use an SMC Barricade router and ORiNOCO wireless adapters in my LAN. The farthest computer is about 40ft away through a floor, a wall and a cabinet and it is locked into the 5.5Mbps zone with an "Excellent" signal... I get awesome speeds from it.. very nice. My other computers are closer; the closest is about 15ft away and it goes through 2 walls and a cabinet and is locked in at 11Mbps with an "Excellent" signal is _VERY_ fast!
So, fool with placement, tweak the router with the increased power hack and if all else fails, I highly recommend the ORiNOCO adapters as will 99% of everyone in here.
Good luck,