The mounting points are there for the seat fixings, you just need to acquire 4 fixings for the outside seats to move (as attached photo)
Seatbelt wise, being a 2001 you may or may not have the big hump in the headlining between the rear two seats. Unfortunately I don't have a photo to hand but its obvious if you do - if you don't then as Greg says you'll need to get a centre seat with a lap belt. If you do then the mounting point and metalwork should all be in place under that hump for another seatbelt real to be be installed. Finally, you may need to make a few enquires with your insurance company just to make sure there is no problem as it will be registered as a six seater.
All in all isn't a big job, just time consuming taking everything apart! I did a 2004 car in 3 hours but then I've taken Galaxy's apart many times before
Parts wise:
4 Runners/Fixing Points
1 Seat
1 Seatbelt
1 Plastic seatbelt exit point to be cut into the headlining
1 7 Seater Carpet
