I don't have the Medtronics, I have the Codman (used to be Arrow). There are big differences between the two - the most being that the Medtronics has to be completely replaced every 5-7 years because it runs off a battery. The Codman works on hyrdrolics and is expected to last a lifetime. The dosage in the Medtronics can be changed a little easier and set to deliver different strengths at different times, while the Codman is a constant flow of a specific dose. I'm young (mid 30's) so the Codman was a better option for me so I won't have to have surgery every 5-7 years to replace the pump.
You'll go through a trial of the pump that lasts about a week and is to make sure you have no complications from the medication being delivered directly into your spine. After the permanent pump is implanted it can take months to get the dose where it needs to be, so this is not an over night solution. It's important to discuss placement of the pump with your surgeon - too low and it's right at your pants waist band, too high and it's up under your ribs.
If you search the board you will find a ton of threads about the pump and a lot of great information. If you want to know anything specific - please let me know and I'll try to help any way I can.