wait, in the actual email it shows that, or in the "full email" which includes a bunch of jibberish at the top and bottom?
if all your emails come like that normally, then i dont know what is wrong, gmail disables you from typing html, so if the sender is trying to use it, it wont work. the only way html works in gmail is by copying and pasting the actual product of the html (such as copy/paste from a WYSIWYG)
if that was too confusing, let me try organizing my thoughts a little more...
Gmail rarely allows you to send html, but it does allow you to recieve it. However, only certain html can be recieved. The <head> tags and such are not neccesary in emails, and gmail probably disables them. If every single email from every provider (yahoo, hotmail, gmail, etc) shows up llike that, then I do not know.
hope that helps.