Yeah, the 50 1.4 will also do well in low light.
You MAY not need to use the flash.
Depends on the gym and it's lighting, yes/no on flash use, blah blah blah.
The D80's kinda notorious for not doing so well with low light noise...
Hehehe...I'd look at the first batch of volleyball shots as 'practice/warm up' shots.
Try out different iso's with all your lenses and run the pics through a post process edit to see how the noise factor shows up when you blow up a shot to 50% or more.
The darker areas of your shots will tell the tale.
That should give you an idea of your iso limits and how you want to set your camera up to compensate for noise.
(one more reason to get the jones goin' for the D7000...
)