Unless there is some strange functionality you need from VMWare that isn't supported in VirtualBox, I suggest giving it a try.
FTFY
You do have to re-enable the source manually - it's not deleted, but the 9.04 -> 9.10 upgrade process turns off third party sources as a precaution.
Just finished upgrading an AMD quad core box, smooth sailing.
Unless there is some strange functionality you need from VMWare that isn't supported in VirtualBox, I suggest giving it a try.