Here's my experience.
If you're in the northern hemisphere (which you are
) the point of star rotation is around the north star. Very easy.
If you're in the southern hemisphere, find the southern cross, and 'copy' its height 2.5x below its tail - that's the rotation point.
You'll start to see the effects of rotation become prominent after 5 minutes. A full rotation is 24 hours (kind of logical) - so you get 1 degree of turning every 4 minutes. Obviously the stars further away from the rotation point will appear to move further, but that may not be the effect you're looking for.
Best piece of advice w/ star trail photos is that you probably want a decent subject in your foreground. Use the widest lens possible to maximise the effect, find some nice foreground, shuffle around til you get the point of rotation right, and then off you go.
It's a nice effect, easy to have too much of it though.
One of my favourite shots is
The guy who takes it is a master photographer (and I don't give that term lightly) - he has a terrific page with good, to the point information:
http://www.danheller.com/star-trails.html