Before you registered for the exam you should register for an account at Linux Professional Institute. After you register you’ll receive an unique LPI ID which you must provide (also with a valid ID card) at the exam center for proper identification.

Exams can be taken on Pearson Vue or Prometric Testing Centers. You can locate a Vue testing center or look-up for a Prometric test center.

I found Vue’s site more user friendly and the information more easy and more quickly to find, but this is just a personal opinion. On the other hand, it is possible that Prometric to have a testing center more close to you than Vue. It is better to take a look on both websites, to analyze data and to take the right action, convenient to your needs. The prices are similar for both providers, at least for my country. The difference is that on Vue’s site you can register for all three exams at any time and on Prometric’s site candidate must successfully pass either LPI 101 or 102 before booking for the second LPI exam and the Ubuntu 199 exam can be booked at any time.

Vouchers are valid for 12 months from date of receipt so, there is enough time to learn and to prepare for successfully passing the LPIC-1 and UPC exams.

Update, 06 June 2010: The link to “special offer exam” is dead. But the offer is still valid, and the link to “the online form” is still active. Good luck.