What would be a good set up for shooting night sports?

I'm running a Nikon D3100 currently with a 18 to 55 lens.
The other night I was photographing some of my good skier friends doing this rail at night (urban skiing). I was shooting with a Shutter Speed around 1/250, Aperture: f/4.0 and ISO on auto. My friend also lent me his really old flash which produced practically the same result as my build in flash. The pics turned out decent but I still think I can get them better…

I was wondering if anybody with any experience or knowledge could help me out in selecting the proper ISO, Aperture and Shutter Speed…

Also if you could advise in order what upgrades I should get for my camera (eg: flash, new lense (what type?), etc.

Ok… Good sports shots are really hard to get.

You'll need some fast glass like a 70-200 f2.8.
you'll need some heavy duty STROBEs… Not the built in flash, not s a show mount flash bu a slaved massive strobe.

Take a look at this guys blog.

http://markhancock.blogspot.com/

He specialisez in sports photography.

I strongly recommend setting your camera setting to Manual to get the most out of it's capabilities.
But if you want to shoot with auto ISO, change the dial to Night Portrait. If you want to manually set your ISO, it's mainly trial and error. It depends on how well your light source is and etc, but I usually stay within the 200-400 range. Play around with it until you get the exposure that you prefer.