Have you tried:

'ipconfig /release'
'Reboot'

The reboot SHOULD give you a new IP-adr based on the correct vlan/MAC-adr.

I don't really belive this will work, beacuse:
I have had some strange results in WINS/DNS, when using a different name for a workstation that is reenroled to the domain on a different subnet or with a new name.
DHCP 'knows' the ws in advance by MAC-adr, so the old lease/IP-adr is used even for a different subnet.
Even worse, sometimes WINS is not updated correctly, and other times DSN is not updated correctly.

You might even have the ws registrered twice in DHCP with different ws-names, but registrered by same MAC/IP

The bullitproof method for me is to remove all entries in DHCP/WINS/DNS. I know you can't do that, so this is just a suggestion for a trial an error method, might work/might not.

Maybe someome with greater insight in the naming protocols can add to this.

-Erik