Is it possible to have two bibliographies in Word 2007? I want to use the first one as a reference list to external references and the second one to be a list of my own appendices.
If you are talking about the Word 2007 built-in bibliography tools, then no. They are basically just field codes, so putting the same field in twice will give you the same result twice.
But do you need two bibliographies? It might be possible to use one bibliography and just split it in two parts. It won't be easy, but you could write an xslt sorting routine to take care of it for you.
For a basic guideline on writing a bibliography style, see http://blogs.msdn.com/b/microsoft_office_word/archive/2007/12/14/bibliography-citations-1011.aspx