I'm not sure of your intrepretation of multivlan. MultiVLAN means having a port in more than one VLAN without configuring it as a trunk. Only our XL switches support multiVLAN ports and CAT4006 does not.
If you want to pass more than one VLAN to another switch, you have the option of configuring it as a dot1q trunk. Also some NIC cards support trunking too. You can find more info on trunking on CCO at
http://www.cisco.com/warp/public/473/#Trunking
If you are looking for any layer 3 features on 4006 with Sup2 engine such as inter-vlan routing, yes you'll need a Layer 3 module or an external router. If you have a Supervisor 3 engine, you'll not need Layer 3 module or an external router.
Hope this helps