Sun VirtualBox or VMWare for a virtual ISPConfig?

[make-fun]

Hi folks

Here is what I'd like to achieve:
A VirtualMachine with Ubuntu 8.04, running ISPConfig(v3 when it's ready)
Why:
Need to be able to move hardware frequently, but wanna run a steady and well tuned system.

This extends also to the question whether it'll be Linux or Windows based?
In the past two years I had to setup our Linux-Server and ISPConfig seven times, due to ISPs issues!! On the other hand we had another very reliable ISP providing a Windows-Server… so I could maybe just run one Server… as neither of the two physical machines have a big load at all.

So far I got some experience with VMware-Server and the VMware-Player on the Windows side, using them in a teaching environment with LAN access only. The Server seemed rather slow, so we used the Player once the VMs were built — no experience with VMware-ESX.

Questions:
Windows-Side:

• A Windows-Server 08 with 2GB RAM should be sufficient, right?
• How does it work when your ISP gives you only one IP and the Windows-Server already has the IIS running, providing needed HTTP & FTP?
  (Email, some more websites, MySQL etc. will run in the virtual sys)
• Would an Image with Ubuntu 8.04+ISPConfig set to ~1GB RAM run well in the VMware-Player
  (neither of the two have high loads and I ran Ubuntu 6.06+ISPConfig on 512RAM just fine)
• Any good reasons for using Sun-VirtualBox — I tried 2.0.2 and it crashed a lot…!?

Linux-Side:
(Here the base would be an Ubuntu 8.04 Server(1.5GB), running a virtual Ubuntu 8.04+ISPConfig set to ~1GB RAM or more!?)

• How is VWware on the Linux-Side? I've never tried.
• Would the Sun-VirtualBox (headless) be the better choice? Strong points?

I'm mostly seeking information and experience on how this works and behaves in a production environment, as I'll step out of our tiny LAN…

Thanks in advance

Cheers