There has been an explosion of manufacturers producing 3D graphics accelerator cards for personal computers. These cards (as of September 1996) perform in the 500,000-2 Million polygon per second range, and vary greatly in cost from 300 to20,000 (and the cost does not necessarily correspond to performance!). Don't go out and buy 3D graphics accelerator cards too soon, noted NASA VR researchers are currently working with many 3D accelerator companies trying to get the "perfect" performance from desktop PCs. Silicon Graphics has developed "new" desktop versions of their graphics powerhouses that might speed up the development of VR with less expensive setups.
There are also several manufacturers producing 3D sound cards. These sound cards allow you to give a moderately good sense of position to a small number (1-4) of independent sound sources; however, the best is yet to come. With the advent of VRML 2.0 on the Internet, 3D sound is becoming something of a must.