WAP location, antenna orientation, channel selection

[BCinSC]

Got a WRT54G connected to cable modem in office over garage. Running ethernet to main part of house and putting WAP54G there. Should the two be on same channel? If I put WAP54G in attic, should I put one or both antennae horizontal?

 

[Cooky]

I believe the two AP's should be on different channels. Those are omni-directional antennas and therefore, should be all vertical.