Steering on 2005 vectra gets stiff when wheels are straight almost 2 the point of locking up is this the steering rack knackered or power steering issue 

I would look at the Strut Top Mounts as these can cause the issue you are describing.

If you raise the front of the car (both sides) and then turn the steering from lock to lock and if it doesn't bind then that is more than likely the problem (since the weight has been taken off the mounts).

It will also give you the opportunity to see if there are any other points where the steering in binding

Thanks I will have a look