davey, thanks for your reply!

why are you using exp / imp when you should be upgrading the database using the upgrade scripts.
Because it seems to me, that the full exp/imp way is the most flexible one.

Could you please explain, what do you mean with "upgrade scripts"? Where can i found them?

Anyway if they are on the same box you must pre-create the tablespaces as it will try and create and create them in the same place as the ones that already exist. Will all work after that.
Ok, but how will the users and be created? Because the "create role" and "create user" statements aren't in the export file which we created from 8.1.7.

I presume that you are using the correct version of exp / imp for your versions as well
Yes, i'm using exp from the 8.1.7 database and imp from the 9i db.