I have a 99 Infiniti G20. I was looking to upgrade top speed and acceleration. I was told a turbo was good.

It is alot harder than just adding a turbo. You must do some engine work to accommodate for the added pressures on the engine along with running PROPER oil lines for lubrication. It is an involved job and one better left to a professional. G20's never came turbo charged in the US so a swap is almost impossible unless you get it overseas from a Japanese model similar to your engine.