A Melbourne woman accused of killing her lover confessed to hiding sleeping pills in his pepper steak then smashing his head in with a fire poker as he slept, a court has been told.

The woman, who can't be named for legal reasons, is on trial in the Supreme Court of Victoria for the May 3, 2005 murder of her partner, whose body has never been found.

The court was also told on Wednesday the woman told another person she slit the man's throat as they had sex and "it was the best orgasm I ever had".

It's also claimed she told two more of her lovers the man was now under the sea, "swimming with the fish" and she sometimes "sang about it a little bit, in a happy sort of way" to one of the men.

The court was also told the woman said she had help disposing of the man's body, dismembering it and dropping it into Port Phillip Bay.

She allegedly claimed her partner had been violent, raping her "with a number of his mates", locking her in a cupboard and raping her dog.

In his opening speech to the jury, crown prosecutor Andrew Tinney SC said the alleged admissions showed the woman was involved in some way in the murder, although the details varied.

He said she either killed the man herself or took part in a "joint criminal enterprise" with another person.

Mr Tinney said the woman had been having an affair with another man while still involved with her now-deceased partner.

He said on the night of the man's disappearance, the couple had friends over for dinner.

The woman and a female friend cooked the man's favourite dish - steak with pepper sauce and vegetables - and the friends enjoyed Greek brandy together, getting "tipsy".

With the pokercc man watching television on the couch, the friend said she returned home about midnight, taking the woman with her.

The friend said when they returned to the couple's home, the man and his car were gone.

Mr Tinney said after the man's disappearance, the couch had been moved to a back room and was later found to contain bloodstains matched to the man's DNA.

Mr Tinney said one of the woman's friends said she described the dead man as an "arsehole, was very violent towards her, did sick shit" and raped her dog and drugged and raped her.

"He got what he deserved and I enjoyed every f***ing minute of it," Mr Tinney quoted the woman's friend saying.

The hearing before Justice Jane Dixon continues Friday.

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