The S13 can use aftermarket hubs up front and rear. Another configuation is aftermarket front and S14 (or 300zx) 5-lug rear. You should replace the hub seals when you do this. No other parts are required.
If you want to go all OEM, you'll need S14 lower control arms with the ball joints in addition to the S14 hubs for the front. Rear is still the S14 5-lug hubs.
You can press S14 ball joints in the S13 LCA's, but I've heard mixed results under heavy track use.
The aftermarket route was a lot more expensive, but recent brands like S5 and Ichiba have brought the cost down considerably.
I will probably go with GTO or Attain hubs for my S13, but I have all the parts (except good LCA's) for the 5-lug swap, which cost me around $300, including the almost useless S14 calipers.
Search around and ask people about their swap experiences.
Here is a post that I just read that has some information:
http://www.sr20forum.com/240sx/166957-s14-hub-s13.html