Oracle Connection Problem

The setup to my problem is a bit lenghty but I try to keep it as short as
possible.

We have a VB6 application that connects to an Oracle 10g DB. We use the
OleDB providers from both Microsoft and Oracle to connect to the database in
order to take advantage of the various quirks of each provider. So far we did
not have any problems. Recently, I had to install the full version of Oracle
(10g Personal Edition) on my machine to demo the app to a client and since
then I can no longer connect to the database (on the server or the local
machine) using the MS OleDB provider. I get an "error in initializing
provider" error with no additional information.

We are using MDAC 2.7 but changing the reference to 2.8 did not help. The
local machine has Win XP SP2. I tried to reinstall the data access components
but I can't find the necessary download that would work with XP SP2.

Does anyone have an idea how to fix that?
.