Best place to put wireless router.... (house)?

Hi, i'm having some problems with my connection, i have a NETGEAR rangemax wireless router (model WPN824), i live in a 2 floor house, and the computer is on the 2nd floor (next to the router), above the entrance of the house, and i use the laptop on the 1st floor, in the living room a few meters away the router, but when i am using it in my moms room (1st floor, like 6 mts away from the router), or i use my pda in my room (2nd floor, 6 mts away from the router, its difficult to keep the connection on, what can i do, should i put the router in the 1st or 2nd floor, or in the center?