Frank, if your van is a US model, it should be easy.  If it is a
Canadian model, you may want to read through Richard Atwells comments
at http://www.ratwell.com/technical/Importing.html under his section
 From Canada to USA:

You will for sure need a smog test done (has to comply to California
OR US49 state emissions).  The smog testers look at EVERYTHING during
their visual check, it must be stock, and most California smog places
in the Bay Area are quite familiar with Vanagons.

If you are missing one vacuum hose you will fail.  If you don't have
the yellowish US emissions sticker (behind the license plate door on
90's) you will most likely fail.

If your van is Canadian, I suggest you replace your Burgundy license
plate door with the same color US door that has the US emissions
sticker on it.  Also, remove any Canadian emission stickers from your
engine bay.

You will also need the VINS verified by the DMV or CHP (easier at a
DMV, CHP often requires an appointment 2 weeks in advance)

-Paul