Help with taking sport pictures

I am a beginner and have a nikon D80 with a 18-135mm DX-AFS and have taken many fastpitch softball and soccer pictures with some success...I was unable to take pictures at dusk or early evening so I have invested in the nikon 80-200mm f/2.8 ED-D lens (will arrive Monday)
With a fixed 2.8 what settings should I start out with in regards to priority modes. As a beginner would it be best to put it on Aperature priority and let the camera determine the shutter speed?
With my 18-135 I would use shutter speed priority with a shutter speed of 1/500, ISO 200 and the camera zoom set the aperature...

Looking for advice before having to re-invent the wheel....

Your advice is much appreciated