What do I have?

The front bumper is the easiest way to tell them apart. the 400 bumper is rounded and the 450 bumper has to straight cross bars.
Here is a picture of my bike which is a 400 frame. <a href="http://www.dirty4man.com/images/ourbike" target="_blank">http://www.dirty4man.com/images/ourbike ... OMBASH.jpg</a>
here is a picture of a 450 foreman front end
<a href="http://www.hondaforeman.com/phpBB2/file" target="_blank">http://www.hondaforeman.com/phpBB2/file ... rs_107.jpg</a>

Great! Going by the pictures it is a 450. Can anyone tell me if I'm right about it being a 2002? Thanks.

478 means it's a Honda ATV made in USA.
10th digit is the year. Yours is a 2002.
11th digit is the assembly plant. 4 means South Carolina
TE220 refers to the model. I don't know which model this code represents but my 400 is a model code TE202.

Hope this answers some of your questions.