It is not a partiularly useful 3D view feature yet. The components have a field to define component height; however, the 3D viewer displays only internal default values. You get a pretty picture, but it isn't an accurate display - this is yet another D*XP feature that needs to be completed/fixed in a future service pack-it hasn't been fixed as of service pack 2.
You still can't control the displayed component heights in SP3 pre-release. The component heights displayed in the 3D view are default internal heights defined by Pr0tel.
The 3D view won't be really usefull until you can create your own components with working component height information, or modify the heights of the provided library components. There is a parameter box for height in the component properties, but it doesn't actually do anything yet.
There is also another program called View3D addition part for 99SE,you can not only see what PCB is like ,you can also export the mechenical data to some 3D software such as UG,ProE,SolidEdge.
but this software is not designed by Altium(protel)