Who assisted Chinese rebels in overthrowing the Ming dynasty and installing the Qing dynasty?
The Manchus played a big part as well as individuals like Li Zicheng.
At the time of the revolution, there were still many tribes within China. In Manchuria (North East China) the tribes (known as Manchu) united to try and change China. The reason for this was largely due to the unpopular taxation imposed by the Ming dynasty.
The Manchus weren't the only people unhappy, though, and many rebellions had broken out. These rebellions were led by a peasant soldier called Li Zicheng who captured Beijing in 1644 and established the short-lived Shun Dynasty there.
Ming officials then turned to the Manchus to ask for help defeating the rebels, but instead of helping, the Manchus actually seized power for themselves. A large army under a Manchu prince named Dorgon captured Beijing from Li Zicheng and took advantage of all the conflict to set up their own dynasty - the Qing Dynasty.
I hope this helps; let me know if I can do anything else (I do love Chinese history!) :D