I'm going to be doing my build on the 29th October and I'm slightly confused when it comes to fans. The case I'm going to use if the HAF 912 Plus and I'm not sure if the fans are 4 or 3 pins. So, my question is can you plug 3 pin fan connectors onto a 4 pin header? And what about the other way round?
Yes and yes is the short answer. There is however a strong argument for running them directly from the PSU. You can use a fan speed controler, or in line speed redusers, or just buys quiet fans in the first place and run them on 12V. By not running them from the motherboard to remove some of the stress from the motherboard. There is a question as to if the motherboard can surply 12v and if it can should you? Should you be plugging in such primitve electrical things as fans in to something as sensitive as a motherboard?
Personaly I run my fans with redusers from molex direct from the PSU. Leaving my motherboard to do all of the fancy electronic stuff.