While you *could* potentially swap in a 4WD transmission, it's a major undertaking requiring significant mechanical expertise and a substantial amount of parts beyond just a transfer case. You'd likely need:
* A 4WD transmission: The correct one for your vehicle's year, model, and engine. This is not a bolt-on part.
* Driveshafts: Front and rear driveshafts compatible with the 4WD transmission and transfer case.
* Differential: A front differential, unless your vehicle already has one (unlikely if it's originally 2WD).
* Transfer case: This will connect the transmission to the front and rear axles.
* Wiring and computer modules (potentially): 4WD systems often require electronic control, and your existing system might not be compatible.
* Mounting hardware: Various brackets and mounts to properly secure the new components.
* Possibly the front suspension components: Modifications to the front suspension are usually needed to accommodate the added weight and stress of four-wheel drive.
This is a complex and expensive project, best left to experienced mechanics. The cost of parts and labor would likely exceed the value of most vehicles. It's generally more practical and cost-effective to purchase a 4WD vehicle directly.
