Serbia goes to the polls this Sunday, in an election which could decide on its future integration with Europe or isolation. Vojislav Kostunica heads one of the pro-democracy parties - DSS - which united to end the Milosevic regime three years ago. Boris Tadic heads the democratic party DS. It was led by the late prime minister Zoran Djinjic, who was murdered last March. Tadic has said the election means choosing between returning to the chaos of the past or building a constructive future. He has appeared with Djinjic's widow. The G-17 Plus party is led by Miroljub Labus. G-17, DS and DSS worked hand in hand to reform post-Milosevic Serbia. Analysts say that in spite of disagreements, these three parties should be able to prevent the ultra-nationalists from grabbing power. Opinion polls, however, predict that widespread discontent about economic reforms will hand about a quarter of the vote to the hardliners. The international community is concerned about the wider effect the elections could have on stability. A political shake-up could threaten the partner-status only recently hammered out between Serbia and Montenegro, for instance. The head of the ultra-nationalist Radical Party, managed to telephone his Belgrade headquarters from behind bars in The Hague. Vojislav Seselj was defying a campaigning ban imposed by the U.N. war crimes tribunal. The ex-paramilitary leader is accused of atrocities during the wars that tore apart Yugoslavia in the 1990s. He and also-indicted ex-Yugoslav leader Slobodan Milosevic - who heads the candidate list of his Socialist Party - were forbidden to campaign after Milosevic broke detention rules. He had taped a speech which was broadcast by a Belgrade radio station. The radicals say Seselj's call showed important support coming just ahead of the election. **PHOTO CAPTION*** Vojislav Kostunica , the last president of the former Yugoslavia, and DSS-Democratic Party of Serbia frontrunner gestures during the final pre-election rally of his party, Thursday Dec. 25, 2003 in Belgrade, three days ahead of a key parliamentary elections in Serbia. (AP Photo/Srdjan Ilic)