Hi, you can "jump start" a starter to check this one and to eliminate the
ignition switch possibility... are you willing to do so? if yes, you need a
long wire (8-10gage) of about 10 feet, go under the van, hook up this one
where you see a red (the smaller one) wire on the starter,
http://www.benplace.com/85rouge/rouge134.jpg
(the red wire on top of starter, on left with the white plug at the end)
go out and touch the + batterie, this will mean that the starter IS spinning.

Like someone else stated, it could be the neutral safety switch if it's an
automatic, or, i'm pretty sure, it's can and may be the ignition switch.

Here is what we mean by ignition switch:
http://www.benplace.com/dash/dash12.jpg

Full section on how to do the job yourself is here:
http://www.benplace.com/dash.htm

Good luck
Ben