how do you switch between wireless networks?

[BSD baby]

> >I just got my wireless connection working with a new PCMCIA card.
> >But I'm still naming the wireless network in my rc.conf file. (DHCP 
> >connection)
> >But as I go to join other wireless DHCP networks around the world,
> >what's the best way to switch to that network without rebooting to do it 
> >from rc.conf?
> 
> ifconfig <interface> ssid <ssidofwirelessnetwork> <ip> netmask <netmask>
> should do that trick without rebooting.


What I couldn't find in the handbook was how to do this for DHCP?

If I don't know the IP or netmask, and want to let the DHCP server decide,
how to I tell that to ifconfig?