How to place text in the clipboard so that it pastes as a table in Word?

The Windows clipboard supports multiple formats. When you want to place things in the clipboard, you make one or more calls to RegisterClipboardFormat() telling it the formats of the objects you will be placing on the clipboard, followed by calls to SetClipboardData() which actually places the data into the clipboard.

If you want to be able to paste a Table into Word, then HTML is the easiest format to work with. Just copy an HTML table onto the clipboard, and it will paste correctly into Word, provided that you first register the clipboard data as an HTML object.

I'd give you some code, but it's easiest to just reference an example on MSDN:

How to add HTML code to the clipboard using Visual Basic

This page even shows an example of copying an HTML table onto the clipboard.