I have a scenario I would like opinions on:

I would like a LAN and WLAN and have the WLAN accessing only one domain, while the LAN can only access another. I've disregarded the 2820N as the wireless device, as it's not compatible with the devices I use - so will be getting a separate WAP.

I understand the VLAN feature could make the ports mutually exclusive, so I'm thinking I'd need that, and obviously I can configure the firewall to block the access. But how to block access per port?

So,
P1 - to allow access to *.google.com
P2 - to allow access to *.bbc.co.uk

I see there is a feature under Applications on the 2820 'IGMP' that looks tantalisingly close to what I want - any suggestions?

VLAN is used to separate or group the Ethernet ports (at Layer 2). It is not IP aware and not application aware. The content filtering facilities apply on the WAN connection so are not Ethernet port specific.