Of course I did not 
The old wallet.dat file is still backed-up on several usb sticks and since no transactions have been done since installing the new wallet, I suppose they should still work.
So I should go for deinstalling Bitcoin client from my pc, delete the new wallet.dat file, download again bitcoin client, deleting that new wallet.dat file as well, putting the old wallet.dat file in that folder and open the bitcoin client?
If I do that, I suppose it will still ask for a password when I want to do a transfer, but this will be my old password isn't it?
And if I am not misstaken, the old password should work like it has always done.
Am I right in these assumptions?
Thanks!
Clochard
The old wallet.dat file is still backed-up on several usb sticks and since no transactions have been done since installing the new wallet, I suppose they should still work.So I should go for deinstalling Bitcoin client from my pc, delete the new wallet.dat file, download again bitcoin client, deleting that new wallet.dat file as well, putting the old wallet.dat file in that folder and open the bitcoin client?
If I do that, I suppose it will still ask for a password when I want to do a transfer, but this will be my old password isn't it?
And if I am not misstaken, the old password should work like it has always done.
Am I right in these assumptions?
Thanks!
Clochard
No need to deinstall the client. Just rename your new wallet as newwallet.dat and move a backup old wallet named wallet.dat into the folder. Restart bitcoin-qt and you should be able to use the old password to change the password on the wallet.