>All looks so complicated!
Let me try to simplify it.
In Office, before 2007, if you saved a powerpoint presentation it saved it with an "extension" of PPT, so for example the name may be Salespitch.ppt
In Office 2007 Microsoft decided to change the format of ALL their files, so in Office 2007 when you save a Powerpoint presentation it saves it with an extension of PPTX, so Salespitch.pptx
The problem is that Office XP has no idea what a PPTX file is, so it wont work.
So you have 2 choices:
1) Save the presentation as a "PPT" file (Office XP format)
2) Get the other person to install the compatibility pack on Office XP so it DOES know what a PPTX file is.
That is about as simple as I can explain it.