5. When I attach a Word document (or an Excel spreadsheet, or a .JPG) and try to open it I get an error message that says: "The system cannot find the path specified." This also happens with incoming emails with attachments.

First, if there is any anti-virus program or any email monitoring (anti-spam) program running on your computer, please temporarily disable it and test the issue again. If the issue persists, rebuild the file association for the files following the steps in the article: http://support.microsoft.com/default.aspx?scid=KB;EN-US;307859

6. Sent mails with attachments seem to just sit in the Outbox but the recipient gets multiple copies.

How big is the attachment?
Have you checked with your ISP to see if it exceeds their limits?
Have you checked with the recipient's ISP to see if it does the same there?

Finally, installing a mail proxy and sending through that proxy will help you. You can find a lot of free email proxies at http://www.tucows.com and other download pages.

7. How do I stop Outlook blocking attachments? (And how do I access blocked files?)

Slovak Technical Services, Inc. provides a free Outlook add-in to keep control which attachments should be blocked and which not:
http://www.slovaktech.com/attachmentoptions.htm

8. Links to attachments appear in different places (in the body of the message and in the header). How do I show them always in the header.

The link to an attachment will appear in the body if you compose your message in Rich Text format and below the Subject line if you compose in Plain Text or HTML.

9. How can I access or change the Temporary Attachment Folder?

Microsot describes the way to change the location: http://support.microsoft.com/default.aspx?scid=kb;EN-US;249793

10. I am trying to send attachments from Outlook 2002 to someone who uses Outlook Express 6. They can't see the attachment from within their email

Microsot describes the way to change the location: http://support.microsoft.com/default.aspx?scid=kb;EN-US;249793