Hi, My name is Eric Moyers. I am a Network Support Engineer in the Cisco Small Business Support Center. Thank you for using the Cisco Community Post Forums.
If you are going to keep the AP541N connected to a switch on your network, then you do not have to use WDS. WDS is only needed to connect two wireless devices together wirelessly.
For the setup that you outlined. Set the router up as normal and assign SSID and security. Then setup the AP541N in AP mode. Use the same SSID and security, however I would then assign each device to a different channel.
This way when you search for wireless signals you will see two separate signals. If they were on the same channel; with same SSID and security some times it will only show as one and you will never know for sure which one you are connecting to.
Now for the seamless part of your question. With small business devices you will not be able to get true seamless roaming. That is only available with devices that use a wireless LAN controller (WLC).
Without a WLC any wireless clients would have to disconnect from one signal in order to connect to another. To minimize that disconnection time, it is best to configure any wireless client to have both SSID profiles listed as preferred networks and to automatically connect when in range.
That way the wireless client when it disconnects from one will automatically see the other and initiate a connect.
I hope this helps. Please feel free to ask any other questions as needed.
Thanks
Eric Moyers
Cisco Network Support Engineer
SBSC Wireless and Surveillance SME
CCNA, CCNA-Wireless
1-866-606-1866