would 550w psu be enough to power the machine
Depends on what else is going in, in terms of HDD, optical drives, PCI cards, attached USB devices, etc.
Use a power calculator such as
eXtreme Outer Vision - eXtreme tools for computer enthusiasts - my thought is to increase the answer by at least 50% to allow for expansion, and the fact that it is better to run a powerful PSU at low capacity than a low-power PSU at high capacity.
SD