Are you pasting into a blank document? Try removing the email format before pasting. To do that, open *Notepad and paste the email contents in that first. Then copy / paste the contents of Notepad into Word. Doing it this removes the HTML formatting from the item so that when you paste it into Word, it is just text.
If there are images that you wish to include with the text, try copying the images separately from text, then pasting them into Word in the appropriate place.
Another thing you can try if the problem persists, or if this seems like it is too much trouble.
1) Close Word
2) Do a search for the file "normal.dot" (don't use the quotes in the search box).
3) When you find the file (you may find more than one) delete them all
4) Open Word
Word will automatically recreate the normal.dot file and doing this may resolve the HTML formatted paste problem.
More about normal.dot*Notepad is found at:
Start --> All Programs --> Accessories -->
