Vehicle rentals in New Zealand?

My wife and I are headed to New Zealand in March and I wanted to see if you knew of anybody down there who did vehicle rentals?  We are looking at renting a pop-top camper van to spend our 2 weeks traveling around the south island.  Any leads would be helpful! Thank you for your help.

 ~ Beau Johnston (www.LivingOverland.com Gourmet Cooking * Travel * 4WD) via email