Microsoft PowerPoint accessibility

Hi,

I'm interested in the general accessibility of Microsoft PowerPoint for 
the creation and editing of presentations. Thus far the information I've
 found on the web has been inconclusive, and I think the opinions of a wider group would be very useful. 

As part of a project I'm working on we're considering PowerPoint as part of a solution for the creation and editing of presentations. The rough idea is that there will be a web based library of pre-approved PowerPoint slides that users can package together to make a custom presentation, which they can further edit or customise offline using PowerPoint. However, if despite our best efforts to ensure the web based part of the solution is accessible it turns out that PowerPoint itself is a problem for some users then perhaps it's better that we consider some other options.

Does anyone have any knowledge of how well PowerPoint works with different assisitive technologies?

How "accessible" is PowerPoint considered to be in practice as an authoring tool?

Or does anyone know of any resources discussing these issues?

Any thoughts or suggestions would be very welcome.

Many thanks,

Phil Spencer.