Multiple Virtual Ethernet Interfaces

For the past few days I've been toying around with the bridge utils
packages and the tap/tun drivers trying to create multiple virtual
ethernet interfaces that can be configured with DHCP off one physical
ethernet card. Is this possible?

Current setup:

tunctl (creates tun0 with unique MAC)

brctl addbr br0
brctl addif br0 eth0
brctl addif br0 tap0
brctl stp br0 off

ifup eth0 (works with dhcp)
ifup tap0 (does not work with dhcp)

System is a vanilla ubuntu server install.

Thanks in advance for any help/guidance.

-Chris