thanks for your reply,
I actually just found this on a google
Cause:The portion of Exchange that converts the outlook MAPI message to the OWA readable MIME message does not know about the new office2007 file formats.
Fix:Add the Office 2007 content types to Exchange so that the conversion process knows about them. This is done through the Exchange System Manager. Each of the content types is a string, and then has a file extension associated with it. You will add the string and the associated file extension to ESM like this:
1. Open ESM.
2. Expand the Global Setting Branch
3. Right Click on Internet Message Formats and choose Properties. This brings up the current list of known MIME content types.
4. You might want to peruse the list at this point and confirm that the office document extensions are not in the list. For example, lets use docx as the extension we are adding for this test. You look and confirm that docx is not already in the list.
5. Click the Add button. CAREFULLY copy and paste the MIME type into the provided textbox (no leading or trailing spaces), and then enter docx in the extension checkbox.
6. OK out of all the dialogs
7. Restart the Information Store Service to ensure that store gets the new list.
8. Restart outlook if it was open and send a new test email with a docx file. Also for comparison sake send a mail with the same attachment using OWA.
9. Use OWA to read both messages sent in step 8. Confirm that the attachment behavior is the same.
application/vnd.openxmlformats-officedocument.presentationml.presentation pptx
application/vnd.openxmlformats-officedocument.presentationml.slide sldx
application/vnd.openxmlformats-officedocument.presentationml.slideshow ppsx
application/vnd.openxmlformats-officedocument.presentationml.template potx
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xlsx
application/vnd.openxmlformats-officedocument.spreadsheetml.template xltx
application/vnd.openxmlformats-officedocument.wordprocessingml.document docx
application/vnd.openxmlformats-officedocument.wordprocessingml.template dotx
P.S. found this also but you may have already done this as well
http://support.microsoft.com/kb/162059