The PPP won the most seats in the national assembly in Monday's elections, while the PML-Q, which supports Pervez Musharraf, the president, trailed a distant third.
In videoOpposition hopeful
In picturesPakistanis head to the polls
BackgroundPower and politics
The PPP wants Nawaz Sharif, the prime minister Musharraf overthrew in 1999, to join the coalition along with an ethnic Pashtun party in the North West Frontier Province where fighters operate.
Taj Haider, a senior PPP member, said: "The dividing line is whether you were with the dictatorship or whether you were with those forces who were struggling for democracy."
Sharif, whose party ran a close second in Monday's poll, has made driving Musharraf from power his mission since returning from exile in Saudi Arabia in November.Mushahid Hussein, secretary general of the PML-Q, told Al Jazeera that his party's election performance was "far below expectations".
"But we are democrats," he said. "And we have accepted our defeat with grace, which is a first in Pakistan's chequered political history.
"And we look forward to working with the future government in the parliament as a robust and vibrant opposition."
"We have a sizeable number. We are a major player ... We expect to play our rightful role in the opposition, and that is something new and different in Pakistan.
"We won't try to destablise the government. We would like to co-operate with the government in promoting a genuine national agenda which serves the interest of Pakistan and its people."
Support losses
Musharraf blamed his poor election performance on sympathy votes for Bhutto, who was killed during the election campaign, inflation, and a battle in the judiciary last year that led to Musharraf sacking the supreme court.
Pakistan vote: At a glance - Pakistan has 81 million registered voters, out of a population of 160 million people. - Voters choose 272 members of the National Assembly, or lower house of parliament, for a five-year term. - Another 60 seats are reserved for women and 10 for religious minorities. - There are 106 parties, 15 of which were represented in the last parliament. - More than 60,000 polling stations were set up across the country. - Key issues include restoration of a full civilian government, reinstatement of sacked judges, rising militancy, economy and high unemployment.But he said the polls were fair.
- Pakistan has 81 million registered voters, out of a population of 160 million people. - Voters choose 272 members of the National Assembly, or lower house of parliament, for a five-year term.
- Another 60 seats are reserved for women and 10 for religious minorities. - There are 106 parties, 15 of which were represented in the last parliament.
- More than 60,000 polling stations were set up across the country.
- Key issues include restoration of a full civilian government, reinstatement of sacked judges, rising militancy, economy and high unemployment.
"We have held free, fair, transparent and peaceful elections. This was my promise, which has been delivered," he said.
"How it is different is that there's a likely change of government. There will be a coalition government that will be coming in."
Despite mounting calls for him to step down, he has refused to leave office, saying he will work with whoever is named prime minister.
"I would like to function with any party and any coalition because that is in the interest of Pakistan," Musharraf said.
"We have to go for conciliatory politics and harmonious interaction within the government, between various parties and between the prime minister and the government. I will strive towards that end. On the other side, I can't say."
"I'm not heading a political party. Let the political parties meet with each other and form a coalition. If any one thinks I can facilitate in a positive way for Pakistan I would like to do it."