Hi,
I've been through two Impromptu to Cognos 8 "migrations".
The migration tools that attempt to upgrade your Impromptu Catalog(s) into a Framework Manager Model(s), and Impromptu Reports into Report Studio Reports.....STAY AWAY!!!!
Simply put, your best option is to rebuild from scratch in C8 and leverage the "intellectual material" from the Impromptu application. (i.e. pretty much use it as a spec/requirement).
First, the tools and the approach are so radically different, there is no way for an automated tool to do a adequate job.
Second, YOU WILL hit "bugs" that you can spent hours and hours trying to fix and then end up deleting and starting from scratch anyways.
Starting from scratch has its appeal! ...for example, you can start/enforce new standards (naming/modelling/etc), and actually leverage the tools the way they are meant to be used instead of throwing back to the way the old tools worked.
....on another note, there is TONNES of documentation with regards to upgrade available on the cognos site. I believe it to be shear laziness that there are people on this forum waiting for other members to email them documentation and the success of their project depends on this. SCARY!
cheers,
david