If you're using VMWare, you make the link a dot1q trunk from your 6500 to the VMware box, then use the features inside VMWare to assign the VM to the VLAN that you want to have it on. I haven't actually done this yet, but have read about it in the Syngress guide for VMWare.
If you're using some other kind of VM software, it might be possible, if the physical hardware can support a 802.1q trunk and properly tag packets bound for the 6500 and decode/detag and route them properly to the separate VMs on the physical host..
