Quick questions:

Is it possible to upgrade my IDM 3.0.1 Engine to 3.5 Engine on NW 6.5
without upgrading the drivers? I'm 99.9% sure the answer is: YES

Once that is done, it is possible to upgrade SELECT drivers to 3.5 (ie,
I want to upgrade JUST the USERAPP driver, not my eDir to eDir driver).
I don't know about this one?

Last question:

If I don't decide (for whatever reason) to upgrade to 3.5 at this point,
when I'm ready to upgrade, can I install another instance of the USERAPP
driver (a 3.5 version), have my 3.0 drivers still be there, and then
setup a new USERAPP server and point it to that 3.5 driver?

I realize that IF that last item is feasible, that I would have to re-
create a lot of stuff that I might have already done.

My main reason for asking is that they want to go live with the userapp
in like 2 weeks and I don't think I will have enough time to test the
upgrades from 3.0.1 to 3.5 in the test lab and then do those in
production AND get the 3.5 userapp all configured by then.