There are a lot of different ways to track a hand or head position and orientation. This is why you can choose whatever method works best for you.
Here are some examples of tracking : http://cb.nowan.net/blog/state-of-vr/state-of-vr-devices/#tracking
There are also cheap ways :
- Gametrak ( position only, should be in the next VRPN release )
- SpacePoint Fusion ( orientation only, should be in the next VRPN release )
- Vuzix VR 920 integrated tracker ( orientation only )
- Camera based tracking (Wiimote, AR Patterns, Rigid body tracking....)
- PS3 Move (soon Sony will release a PC based SDK)
- Freespace (not tested but seems interesting, and already in VRPN)
- Razer Hydra (not released yet but seems interesting)
- < invent your own ! >
As all applications have to use VRPN, there has to be a VRPN driver for the trackers your using.
If there aren't any driver yet, you are invited to write it and share it !