First of all capitalism is a financial system not a political one. Islam has never spoken against capitalism and for proof you can read the Islamic history. Business was the profession of the prophets and many pious people in both pre-Islamic and post Islamic societies. The only thing Islam insists on is a fair circulation of wealth within an economy NOT the creation of wealth.
As far as the political system is concerned, Islam has absolutely NO restrictions. The study of post 632 A.D shows that the methods of governance changed as Islam spread outside the boundaries of Arab tribes. I will give you one such example. When Mecca was conquered, all idols were destroyed to announce the dawn of a new era. People who witnessed it may have thought that it is a part of Islamic governance to eradicate all signs and places of worship once Islam is established in a society.
When Egypt was conquered in 639-640 A.D, Amr Ibn e Aas wrote back to Umar(RATU) and told him about a big statue close to the pyramids and told him that this statue is worshiped by the locals and even a yearly festival is dedicated to it and asked for permission to demolish it. The Caliph stopped him from doing so and you can still see the great sphinx of Giza standing there. The purpose of this example is to establish that Islam has changed its idea of governance based on the locality and time.
In modern day, any Islamic government can be established using the established forms of government as long as the basic principles of good governance are adhered to. You will have to admit that the social norms have changed over the last 1400 years and establishing the social norms of that era in today's society will be impossible.
So all you guys who are sincere about implementation of an Islamic system should stop lamenting democracy and use the current system as the basis of your ideology. These are the basis of an Islamic Government:
1) The welfare of the people
2) Equal justice for all
3) Establishment of a progressive and peaceful society
The moment you bring the social laws of Islam in your idea of government, you will expose yourself to harsh arguments that are almost impossible to counter.