An AP is a share medium, therefore it acts like a hub and every device compite for the bandwidth in it. Each AP has several contentions methods, such CSMA/CA, RTS/CTS (Request to Send / Clear to Send wth ACK) and Polling, but not all the AP's have this three features, at least the two first.
Now, refering to the quantity of nodes for each AP is so crucial ecause you have to now the kind of traffic is going to pass through that AP, in many case Internet and light web base aplications.
However, bandwidth it's not the same as throughput. Bandwidth is the width of the chanell the comunication goes, for example a bandwitdh of 11 Mbps in 802.11b standar equipment, but the througput for this equipment is 5.5 Mbps, equal to 1X of Data Rate.
If you have a 802.11g equipment or AP at 54 Mbps of Bandwidth the Througput for this equipment will be about 27 Mbps equal to 5X.
In that cases you have a maximun (theoricaly) of 10 to 15 Pc's per AP to guarranty a good performance.
In the oder hand, you have to monitoring the implantation of your AP for that quantity of nodes.
Good Luck and read more about design in wireless Lan... it's just a piece of advise.
