Started with a phone screen, then they brought me into the office for an examination and then an interview with the person who phone screened me and another person who I would be working with. The phone screen was around 20 minutes, the examination was around 45 minutes and the interviews with about half an hour each.
After that stage they brought me in for a final round interview with the person who initially phone screened me and the President of the company. It was a 2 hour ordeal that was very thorough.
The best thing to do in preparation for an interview with them is know your resume inside and out. Be confident with both your work and educational experience, do not worry to much about the "test" that will be administered.