Ok, it's now working. :)
I uninstalled Strawberry and deleted the whole Perl installation from my xampp directory. Unfortunately xampp doesn't install an uninstaller for single components so just deleting it now was not really clean. But well...
And my main problem was... I had a 64bit Oracle client. xampp is 32bit and the Perl version I used was 32bit as well. So uninstalling the 64bit Oracle Client and installing a 32bit did the trick.
Thanks a lot for your help all. :)