I agree with Pavel - if it's a small network without a lot of high speed LAN connectivity requirements, then it's probably easier to just connect the AP to your router and put your guest SSID on a separate VLAN. Depending on the router you use of course, it would need to support that functionality. For example we primarily use SonicWALLs, and it's easy enough to add a virtual sub-interface for the VLAN traffic. You would also want to make sure the port on the router that you're connecting to is Gigabit speed in order to ensure the best performance - a number of routers are limited to 100Mbps switch ports, so that may not be ideal. In this option, you would also need to power your AP, so that might mean a separate PoE injector, DC adapter, or possibly your router has PoE capability?
If you already have a switch with PoE and VLAN support, you could also use that. This would be better if you have faster LAN connectivity requirements, such as needing Gigabit connectivity to the LAN for your wireless clients. A lot of PoE switches would provide VLAN support too, so just be sure to verify those two features before you buy (PoE and VLAN support). Good luck!