Berlusconi trial won't leave Naples, court rules
Three-time premier accused of bribing Senators12 March, 13:09
De Gregorio has admitted not declaring to the tax authorities two million euros he received and plea-bargained a 20-month sentence.
The Italian Senate is listed among the plaintiffs. Berlusconi, a 77-year-old media magnate, continues to lead his center-right Forza Italia party, which withdrew from the left-right grand coalition government of then-premier Enrico Letta in November and joined the opposition, from outside parliament.
Prodi's 2006-2008 government fell after losing the support of the Senate, leading to new elections that Berlusconi won.
Valter Lavitola, an associate of the ex-premier's, is also on trial in Naples for allegedly acting as a go-between in the alleged bribery.
Prosecutors have claimed Lavitola tried to bribe other Senators who have not been identified as well.
After 20 years of legal battles, Berlusconi's fortunes began to turn last year when the supreme Court of Cassation handed him his first-ever binding conviction for tax fraud at his Mediaset media empire.
His year-long sentence of house arrest has yet to be enacted. The billionaire is also appealing two convictions by courts of first instance - one for paying for sex with an underage prostitute and abusing his office to try to cover it up; and another for involvement in the publication of an illegal wiretap.
The ex-premier says he has been targeted by politically motivated magistrates since he entered politics in 1994.