If there are only 1 or 2 people using the network, put them on the same channel. They'll take turns, no problem... unless everyone is pulling heavy downloads at the same time you should not notice the difference.
I would check for competing networks nearby, using netstumbler or inSSIDer (
http://metageek.net/inssider ) and use a non-overlapping empty channel (e.g. 1, 6 or 11).