Don't know for sure with IE7 on Vista but all other Windows machines use
MXSML3 for PI invoked transformations. If IE7 on Vista uses version 6 then
they've kept very quiet about it.

At the very beginning of this thread I cited Abel Braaksma which
answered this question. By the way, if you install MSXML6 on
non-Vista, then it becomes the default for both IE6 and IE7 - if
I understood him correctly.

To simplify the argument lets assume we have only MSXML 3.0
and MSXML 6.0.

Now my question was a bit different. Maybe you get handed an application
and you have to check if it runs o.k. with both versions of MSXML's
(3.0 and 6.0). Now you run it with IE6 on Win2k and it seems o.k.
Can you tell which version of MSXML was used for the transormation
and how to test it with the other one ?

Above I mentioned a PI driven transformation, but this is the
simpler case selecting the default version. But even here the
question remains, will it run with the other one too?