How to set the default attachment folder in Outlook

To Modify the Registry Setting

1. Click Start, and click Run.
2. In the Open box, type regedit, and then click OK.
3. Locate the following registry key:
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
4. Double-click Personal in the right pane.
5. Change the value to the path you want. For example:
   C:\My Attachments, would set the location to the My Attachments folder. 
   %USERPROFILE%\My Documents, would set it to the My Documents folder on a computer that had more than one user profile. 
   
6. On the Registry menu, click Exit.
7. Restart Outlook.

When you open a new mail message and attach a file, the Insert File dialog box opens to the folder you have specified.