About a year ago i sent a few computers to Amsterdam for research. The
intent was to keep them there for a year while using them in our
research and then bring them back to the US. At that time, i asked
for, and received, a temporary import license after providing a
written guarantee to pay the VAT if i didn't bring them home within a
year.

The research is going well, and i now want to leave the computers in
Amsterdam for a second year. Is it possible to extend the temporary
paperwork for another year? As a last resort, i can call Dutch Customs
in the Netherlands, but thought i'd try this first.

A successful answer must have a link to where i can see an answer that
i can print out. Thanks.

Your question is probably answered in the conditions of your import
licence.  After working with similar cases in Norway, my experience is
that temporary import permits can not be extended beyond their
original validity period.

Besides, computer equipment tend to lose most of its its commercial
value (and it is the commercial value that is of interest to the
customs authorities) in one or two years, and keeping the equipment in
the Netherlands for more than one year will probably reduce its value
so much that you can no longer export it with the same value as when
you brought it in.  As a general rule, exemption from taxes and duties
rely on you exporting something that has not changed its value while
it was "in transit".

The Netherlands customs authority can be contacted at +31 800 0143
between 08.00 and 20.00 CET Mondays to Thursdays and between 08.00 and
17.00 CET on Fridays.