I have a similar issues, I have a 3com 2824-sfp switch and was trying to get a access point setup for the internet. I do not want the access point to have access to our LAN. I am using a older linksys wrt54g as a access point. Using it as a switch with wireless turned on. I created a VLAN1 with everything turn on (set to D) except one port VLAN2 everything off except one port as D talking to AP. My router is on port two, anytime I turn port 2 into uplink (think that mean tagged) on either VLAN my connection to the router drops. Seems like I have tired about ever possible combination, but not setting something up right. any help is appreciated.