My 1997 chevy astro van won't start... It cranks well but won't turn over, we've changed the spark plugs, wires, rotor, distributor, ign coil, both modules and its getting adequate fuel pressure, but still no start. Where do I go from here?

3 things an engine needs to run,Fuel, Spark, & Compression.
Good pressure does not mean its making it to the combustion chamber. Best way to check for this is to crank a few seconds, remove a plug and see if its wet and smells of fuel.
Need to be sure spark is making it to the plugs and its adequite for ignition (Bright blue).
Cylinder compression should be within 10% of each other and proper for engine specs.

tow in to a Ford dealer

fuel pressure means nothing if the injectors aren't actuating, you need to make sure the fuel is going into the cylinder.
is the rotor turning? if not the timing belt/chain is broken
is there spark at the plug?
is there compression in the cylinders?
Is the intake clogged?

Well, if it turns over, but won't fire, something is wrong. I would verify that it is actually getting spark by putting one of the plug wires against the block with an extra spark-plug in it and cranking it over to have a look. There should be a bright, whitish-blue spark with an audible clicking sound. I would also verify that you are actually getting gas into the motor either by looking straight down into the throttle body (with a light) as it cranks or by loosening up the fuel fitting at the throttle body and cranking it for a second or two.
Once you know for sure that there is definitely fuel and spark, I would take a look at the choke and make sure that it is operating properly and is closed when starting.

I'm not a mechanic, but it's either fuel or spark. Since you've done almost everything for the spark & the fuel is ok, it may be a broken timing chain.

Our vehicle is doing the same. It will turn over but won't start. It only does this when it rains, I know this is silly but thats the truth. Its getting spark and its getting fuel?? We have checked it all. We have even had it on a computer to check everything and it says that nothing is wrong? If you have any help please reply back.