Our business model of course allows you to keep using Office 2003 - the software doesn't really expire, " said Mr Capossela, corporate vice president of the Microsoft Business Division.

Many large businesses will have Office 2007 delivered as part of existing IT contracts but small business and individual consumers will need persuading to make the change.

Overhauled user interface

And once people have changed, they will need to master an overhauled user interface designed to give people simpler access to the features of Office.

With more than 400 million users of Office in the world, Microsoft are aiming to re-educate a sizeable audience.

There is also a growing audience for an open source solution: more than 40 million people are using OpenOffice.org, a free, community-built alternative to Microsoft Office

Mr Capossela said: "One of the most compelling reasons to move to Office 2007 is the new simplified user interface, something called the Ribbon. It lets you get at far more of the power of the product."

He added: "We've put in a lot of effort to redesign the interface but to make it still familiar but more natural."

To aid the transition Microsoft has retained all of the keyboard shortcuts in Office 2003 and is providing more than 50,000 help articles online.

The firm also undertook hundreds of thousands of hours of lab research and received the feedback of many of the 3.5 million people who downloaded the most recent test, or beta, version of the software.

"The most common clicks that people do with the product - we wanted to make them front and centre on the default ribbon," said Mr Capossela.

"The ribbon doesn't look too different from the old toolbar. Bold, centred and italic - all those sorts of things are still there."

Mr Capossela said their research showed that the vast majority of users adapted to the new interface very quickly.

"The people who take longer are the die-hard users; the expert Excel user," he said.

Jeremy Beale, head of e-business at the Confederation of British Industry, said: "There will be an impact on training for new software like Office 2007, especially for smaller businesses."

Mr Capossela said the feedback from the beta testing had been invaluable - resulting in one major change as the default ribbon was shortened on screen.

"It's a huge influence for us. You start doing that pattern matching across millions of people. We were blown away by how many people downloaded the beta.

"The beta is a great way of feeling how all the research done in the labs is put into the real world."

Online world

Aside from graphical interface changes, Office 2007 is now much more plugged into the online world.

Documents can be posted directly to blogs, RSS feeds are better integrated into Outlook and there is a vast repository of information on the Office online website.

One of the biggest changes is a new default file format called .docx, which is an XML format.

XML documents are smaller in file size and can be interrogated and queried by other third-party programs. It means documents, tables, graphs and databases can be created directly from existing documents, making the information inside an Word document or Excel document much more useful.

Mr Capossela said: "XML is a lot more robust and secure. It's much harder to break into those file formats and do bad things."

He added: "They are much more interoperable: Third party developers can take that data that has been locked up in the past and can translate it into other forms.

"It opens up a whole developer ecosystem to allow translation from one format to another."

To simplify matters Office 2007 retains the use of .doc formats and any document opened in one format will be saved in the same format, unless otherwise specified.

"Most home users will stick with those formats - it's what they know, it's what they are comfortable with," said Mr Capossela.

The move to XML has also been welcome by the backers of open document standards, who feel it will lead to better interoperability between Office 2007 and Open Office.

The OpenDocument Format Alliance (ODF Alliance) said: "By making it easier for some Open Office users to access files stored in Microsoft's Office Open XML format, it makes it easier for customers to adopt ODF without worrying about the difficulty of tapping into files stored in a proprietary format that others may send them, or that they may have stored in their own systems."

But the Alliance also called on Microsoft to let users save files directly in an open standard.