Website modifications

We are looking for a developer who can make a few quick modifications to our site as required. We need to be able to STOP anyone from a particular state (by state code and post code) from being able to place a bid and to let them know a reason why. We were thinking the following limitations for the required state: 1. When a new member tries to register (gives a warning they can't bid and gives the option to continue) 2. When an existing member logs on it should give a warning that they cant bid 3. When an existing member purchases credit (gives a warning they cant bid and that they can not purchase credit at this stage, However, it should allow us to reactivate credit facilities at a later time if we decide to add new options) 4. when the member tries to place a bid it should give a rejection that they can not bid. The warning message can be the same message and should be editable (we have a Content Management section and it could be added to this section), We need the ability to turn this on and off and to specify the state and postcode details as required. If you have any other questions, please ask.