Capital Expenditure budget - and Purchase orders

Has anyone had experience with working with Capital Expenditure budgets?

We're moving more and more into purchasing within Vantage and are having problems where if a Capital Expenditure budget has been set up for a department and the manager of this department creates a purchase order against this budget it still goes for approval. This is not required as the budget has already been approved.

Also is there a way of limiting the total spend from this budget against a number of different purchase orders?

ie: the IT budget is set at $1 million - throughout the year purchase orders will be raised against this Capital Expenditure budget until it has been exhausted - at such a time no more POs can be raised, unless they go through the standard approval method.