"Along that wall will be a gallery with 150 seats for the press and public," gestured Robin Vincent, the registrar of the Special Tribunal for Lebanon, which is expected to open its doors in Leidschendam on March 1.

The tribunal will be housed in the former headquarters of the Dutch intelligence service, a colossal building with fortress-like security.

The courtroom is to be built in what used to be a spies' gymnasium.

"In the courtroom itself, there will be 70 seats," said the 64-year-old British registrar, who arrived from the United Nations in August.

"It will be able to accommodate several accused at the same time, their lawyers, the judges, prosecutors and the legal representatives of victims."

The tribunal will try those presumed responsible for a series of attacks on Lebanese political and media personalities, notably the assassination of Hariri in a car bombing in February 2005 that also killed 22 others.

NSW Deputy Police Commissioner Nick Kaldas has been appointed to head the UN investigation into the 2005 bomb attack that killed Hariri.

Kaldas will take up the position of Chief of Investigations for the Special Tribunal of Lebanon on March 1 next year.

It will also investigate a number of other assassinations that have had a significant impact on the political environment in Lebanon and the Middle East.

The attack on the Beirut seafront was one of the worst acts of political violence to rock Lebanon since the 1975-1990 civil war, and led to the withdrawal of Syrian troops after a 29-year presence.

The use of the building, which formerly housed 700 intelligence staff, is sponsored by the Dutch state - with some left-over furniture thrown in.

In one corner of the gymnasium, behind a row of windows, a body-building room will be converted into an interpreters' cabin, explains Vincent. Hearings will be translated into English, French and Arabic.

"The fitness equipment will be moved to the seventh floor and will be used by the security personnel ... for them to keep in shape," smiled the registrar.

"Of all the international tribunals in The Hague, the security concerns around this one are the greatest."

The budget of the court, known informally as the Hariri Tribunal, will amount to some $US51.4 million ($A75.3 million) in 2009, 49 per cent of it financed by Lebanon.

The construction of the courtroom on the first floor and six holding cells on the ground floor will cost $US8.8 million ($A12.8 million).

"Don't imagine that there will be six accused simply because we are constructing six cells," said Vincent.

"These are not detention cells ... they will be used simply to hold accused before their trials start (every morning) and at certain stages during the day."

Like all accused before international tribunals in The Hague - the International Criminal Tribunal for the former Yugoslavia, the Special Court for Sierra Leone and the International Criminal Court - the future detainees of the Lebanon tribunal will be held at the Scheveningen prison in a separate wing rented by the UN from the Dutch government.

The facility already holds former Bosnian Serb political leader Radovan Karadzic, ex-Liberian President Charles Taylor and several Congolese warlords.

Currently, a staff of 18 are preparing for the tribunal's much-anticipated opening, including a legal counsellor, a language expert, and a defence adviser.

But in a year's time, the tribunal will have 305 staff, 105 of them in the service of the future chief prosecutor, Canadian Daniel Bellemare.

When in full swing, the court will employ around 430 individuals.

Eleven judges - four from Lebanon and seven from other countries - have already been nominated, said Vincent, but their names are being held under wraps for security reasons. -AFP