This belief (I think the current English word is "meme") is a product of Berlusconi's extraordinary propaganda machine with the help, in this case, of the Corriere della Sera. In D'Alema's case, an article was published by the Corriere that revealed he had a bank account with the Banca Popolare di Lodi to pay installments on a boat. The article was published prominently on the same page that carried articles about the Lodi scandal. Nothing more to it than an invasion of privacy. He threatened to sue the Corriere and may have done so.
As far as the Unipol scandal goes, there is still no proof nor current investigations that high ranking members of the DS are involved despite months of investigation of ex-Director Consorte's movements.
This contrasts with the Lodi Bank scandal which has alleged collusion with high ranking members of the government as well as prominent politicos in Forza Italia, Lega Nord and Allianza Nazionale.
Berlusconi's propaganda machinery has been very effective in diverting attention from his personal alleged criminal activity to non-existent criminal activity by members of the opposition parties.
As I pointed out in a recent comment somewhere, this will follow an established pattern. If Berlusconi or members of his government or party are incriminated for the Lodi scandal, Berlusconi will once again accuse the judges of being politically motivated communists who emit clockwork arrest warrants and turn a blind eye on the "crimes" of the opposition.
What can be reproached to the leaders of the DS is a lack of political acumen in backing the Unipol/ Coop OPA. But then I don't see why one should cave into Berlusconi's smear campaigns and act on the defensive. We are dealing with a brilliant and ruthless strategist who will stop at nothing to stay in power. It's asymmetrical warfare.
Of course if someone in the DS does get incriminated, I'll have no problems bringing it up here.