The right way to do this is to use a real router, or multi-NIC PC acting as a router, with support for multiple internal networks. You'd configure different vlans on different internal ports of the router, and then hang a wireless AP off each such port to provide the wireless service. Obviously, each AP would be configured with a different SSID and security settings.
The real question, though, is what do you gain by doing this? Any decent consumer wireless device will have a wireless isolation setting to prevent your wireless clients from hacking each other.