UK Car Repair: W Reg Vectra, steering rack, power steering

Question
Hi
I have recently purchased a W Reg Vectra and the steering went noisy.I checked the power steering reservoir and it was almost empty.I re-filled it and that cured the noise,but I checked 2 days later and it is half empty again.
I know absolutely nothing about the working of a car.
Any advice would be welcome.

Answer
Clearly the steering system has a leak, it may be as simple as a loose clamp or as serious as a leaking steering rack.  You have to see where the fluid is being lost from then make a repair decision. In the meantime try not driving it. The noise is being caused by a lack of fluid which will damage the pump.