Portal spawning?
http://developer.valvesoftware.com/wiki/Prop_portal
Just use normal I/O to enable and disable a prop_portal.
http://developer.valvesoftware.com/wiki ... vator_name
Name the single cube a unique name, and then set the filter_activator_name to the targetname of the single cube in question. Then for your func_vphysics brush, have it use the name of your filter_activator_name.
At least, that's how I would do the reverse gravity. It's not "gravity" and just a physics force, but in theory it should work/function the same way. If trigger_gravity works for you then go for it, but I didn't think that worked on physics objects.
And as always, make sure the brush entity's flags are set properly. Disabled clients, enable physics objects, etc. If you still have problems, post a VMF of the room and I'll look at it.
well thanks for telling me about the trigger_vphysics_motion, it works now!