Why does a PPTX file convert to a ZIP file on download in XP or Vista???

This is a simple one, but maybe not so simple...I have a PPTX (Powerpoint 2007) presentation up on the web, but when my clients download it, the downloader automatically converts it to a ZIP file.  I cannot work out why this is going on but it's driving the client crazy.

I'm running IE7

Please help!
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I Assume the file goes corrupt after it changes it to zip?
If possible can you give me a download link to see if it also does it to me?
marcgimbrereAuthor Commented:
No it doesn't go corrupt.  If I rename it to pptx it's fine.  And the REALLY strange thing is, if I unzip the Zip, it actually unzips the file and breaks it down into all the COMPONENTS of the pptx presentation.  
Sorry I can't show an example because it's private corporate material...
Ok, fair enough.
One thing you could try is to zip the PPTX before you upload it?
The client will have to unzip it but won't have to bother with renaming and you can even fit multiple PPTX'es in 1 file.
Kind of weird that the file automaticly renames 'itself' into a zip, Could it be the web server not liking PPTX Extensions and renames it to a zip instead?

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Links to PowerPoint 2007 files (PPTX, PPSX, etc) on your web site don't work.
When you click the link, you get 404/File Not Found errors or the browser displays gibberish or offers to download the file with an incorrect ZIP file extension.
The real solution is to contact your webmaster and have the new Office 2007 file types added to the web server's MIME table. You may not understand what that means or how to do it, but your webmaster will.
While you're waiting for the new MIME types to be added, you can include your PowerPoint 2007 files in a ZIP archive. Upload and link to that instead (and explain to users that they'll have to extract your files from the ZIP after downloading it).
See also: http://pptfaq.com/FAQ00189.htm
marcgimbrereAuthor Commented:
Thanks Glenna, it turns out I can do this through my site's control panel and I've added the following MIME types for Office 2007 documents:

docx =>application/msword
pptx => application/vnd.ms-powerpoint
xlsx => application/vnd.ms-excel

And guess what...it worked!

Respond to this and I'll assign the points, thanks

Glad it worked for you :)

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