To remove the pump:
1. Remove the cable from the negative terminal of the battery.
2. Drain Coolant.
3. Remove the trim from the top of the engine.
4. Disconnect all of the hoses from the water pump end only. And make sure that you secure them out of the way whilst you carry out the removal and refit of the water pump.
5. Remove the water pump drivebelt.
6. Remove the pulley from the water pump.
7. Remove bolts from water pump (to get the pump out you may have to tap the pump with something soft and blunt to break the gasket seal).
To fit the new one:
1. Clean the sealing surfaces of all gasket material on both the water pump, (Spacer plate, if used) and block.
2. Using a thin layer of RTV sealant, apply to both sides of the new gasket and put the gasket on the water pump.
3. Put the water pump (and if used, the spacer plate) in position and refit the bolts so that they are only 'finger tight'. (Make sure that the gasket doesnt slip out of place).
4. For your car (VT 5L V8?) you need to tighten the bolts on the water pump to 20 - 27 Nm.
5. Refit any mounting brackets that you may have removed.
6. Refit the pulley for the water pump.
7. Refit the water pump drivebelt.
8. Refit all hoses to the water pump.
9. Refit the trim for the top of the engine.
10. Put coolant in.
11. Connect the battery back up.
(I obtained the information above from the Haynes Repair Manual. If you do not feel confident in removing the pump yourself, I recomend that you either purchase the manual yourself so that you can see the diagrams, etc or get a qualified mechanic to do the job for you.)