The recent Doing Business '2011 report states on page 98 that Belgium has no limit on the maximum length of fixed-term contracts. AFAIK, this is wrong. The maximum length of fixed-term contracts is 2 years (exceptionally, 3 years). In some sectors, this is down to 6 months. My knowledge dates from 2007, but I bet nothing changed since then.
Here's a prooflink from 2006.