Powerpoint Slideshows 2003 vs 2007

[Tolu]

How can I set a Powerpoint document to open as a slideshow regardless of
which version (2003 or 2007) I use.

I am trying to load some powerpoint documents unto a portal and I found that
if I use a computer that has Office 2007, only the powerpoint documents that
were created in Office 2007 would open as a slideshow. All the documents
created in 2003 would open as a document with the menu bar an all which makes
it editable.

Please help

Thanks