From what I know, the Belgian government charters planes from the Belgian Air Force for state visits. Most of the times though, their dry-leased (from Portuguese HiFly) A330 is used for official state visits (it does not have a VIP interior though, as SN usually uses it as a backup in case one of their A330's goes tech or has a C/D-check). In a striking bit of irony, that A330 is used to replace the A310's used before (which broke down all the time) and the A330 used by the BAF breaks down quite often as well. In another turn of irony, the A330 currently used (CS-TMT) is an ex-Sabena plane (and from what I've heard, it still has the same interior as it did when it was flying for Sabena).
All of this aside though, I think the Belgian government would be better of buying an A319CJ from Airbus than leasing an A330 which breaks down almost all the time.