Office 2007 Free Upgrading

Does anyone know exactly what the criteria is to qualify for the FREE upgrade to MS Office 2007 from 2003. I have seen articles stating it’s only available for full retail boxed or OEM, and some resellers are stating the same whilst others say it’s available on volume licences as well.

I telephoned Microsoft UK today to ask them the question and told them I was purchasing a 50 user MOLP for Office 2003 Professional and would I be entitled to a free upgrade. I was told that if I bought before March 2007 I would be. The guy did sound very unsure though so can anyone clarify Microsofts position.

I have tried searching the Microsoft website and can find nothing about free upgrades to office 2007.