If you want the 2WD version of the Pede then its pretty easy. I think the only real difference is the chassis, tires, and maybe the arms? Oh and I think a couple of the linkages are different. They are very similar kits though....just compare the VXL Rustler Exploded diagram with the VXL Stampede. Buy the handful of parts you need from a parted out kit on ebay.
If you want to go with the 4X4 Stampede then you're gonna need alot of stuff. Not really sure what all you will need since I've never owned a 4X4 Pede but I know the differences are much more significant.