Feasibility of moving IIS 6 Win2K3 Server to 2K8 on Vbox

[budgin]

I'm considering moving a Windows Server 2003 IIS intranet web server over to Windows Server 2008 runing 2K3 in Virtualbox. This is an old HP Proliant DL140, 1.5GB, runing a minimal accessed IIS web server (asp, access). The 2K8 Server is a Dell PowerEdge 2970 with 8GB of RAM.
Wanting to know if the new hardware will make up any performance loss and any other information regarding performance and feasibility. Plan on bridging the virtualNIC to the 2nd NIC of the PowerEdge that's not being used.
This 2K8 Server is a DC so I'm concerned with security as well. This is another reason I'm considering virtualization since running IIS on web server a DC is not recommended. This intranet is sometimes accessed from the WAN only by a few external people but it's minimal. Load shouldn't be an issue since the DC and the web server are rarely if ever strained.
Will disk2vhd be able to handle this? I've heard it shouldn't be used on some servers.
If the 2K3 server only has about 30GB being used how large should I make the VHD? How much extra VHD space for best performance?

Any other performance/compatibility/network considerations?

Thank you

[BillG]

Personally I would not run any sort of virtualization software on a DC. If you really want to virtualize your IIS server, do it on another machine, not the DC.