2 questions when using vs2005 to debug PG

I'm using vs2005 to debug PG, and I have 2 questions to ask:

1. I want to add a function to contrib/xml2/xpath.c

   I changed xpath.c, pgxml.sql, pgxml.sql.in at the same time, then I builded and installed as the document said. 

   When I execute "psql test < pgxml.sql", all functions created success except the one I added.

   ERROR:  could not find function "xml_value_index" in file "C:\Program Files\PostgreSQL\8.3\lib/pgxml.dll"

   I rebuild project pgxml, a nd replaced C:\Program Files\PostgreSQL\8.3\lib\pgxml.dll by the new produced .\Debug\pgxml\pgxml.dll

   But remains all the same

2. When I execute a simple select query too see how it works, the concept "Portal" really puzzled me, maybe it's too abstract

   Could you please explain it more specifically?