I have Outlook 2003 and was emailed a pptx attachment. When I double click it, it always asks to save instead of opening it. Docx files open fine. I have the Office 2007 compatability pack installed. If I save the pptx file to my desktop i can open it from there, but not if I double click the attachment. Thanks for your help.
MS Outlook does not normally block PPS/PPT/PPSX/PPTX files. Try this (based on XP but you should be able to adapt to suit OS):
Start Menu > Settings > Control Panel > Folder Options.
File Type tab > scroll to and select PPTX extension.
Click "Advanced" button.
If you see a box entitled "Confirm Open After Download" UNCheck it and click Apply.
Close Folder Options dialog and try again.
There is another known issue that concerns compression of attachments, and may be applicable to you. How to disable "Max Compression" of attachments: