Stars will trail across your D300 sensor at the rate of about 1.3 pixels per second per 100mm of focal length. At10mm you would then get about 1.3 pixels per 10 seconds of exposure.
You then need to find your personal tolerance for trailing, and that needs some experimentation on your part. You may be happy with 3-4 pixels, or maybe just one, and that depends on your anticipated output size.
If you can live with 3-4 pixels of blur you may be able to do 30 seconds of exposure, based on the above formula.
If your scene only includes the sky, then you can take short exposures and stack them together.
I use http://www.astronomie.be/registax/|Registax> to stack non-trailed images, and this is basically the "gold standard" most amateur astrophotographers use. Both these apps are FreeWare.
Registax is intended to try to align your images to remove trailing, which is why a different app would be used if you want star trails.
If your scene includes any terrestrial objects then stacking won't work without some serious cut and pasting because the stars will change from frame to frame relative to the ground and horizon.
September, just after dark, is a good time to shoot the Milky Way near the horizon. Well, it will be near the horizon whether you like it or not . The Milky Way can stand a fair amount of trailing because it is diffuse, but the bright stars will trail if the exposures are long enough.
This is a game of either fine tuning ISO and exposure to optimize all this, or using an astronomical mount that tracks the stars. But a motorized mount won't help if you are including terrestrial scenes.