Quoted from expatics in the hR section

Salary indexation levels

The salary level that highly skilled expats from outside the EEA need to earn before being granted a work permit to work in Belgium will be raised again next year.

Linked to the index of contractual salaries, these salary levels are taken into account before authorising the employment of foreign nationals and work permits for highly qualified expats or executives in Belgium.

Such levels are therefore reviewed each year.

From 1 January 2006, Belgian authorities will allow the employment of expats and grant work permits for foreign nationals based on the following salaried conditions:

that the highly qualified expat — whose employment in Belgium is limited to four years (but can be extended for another four years), even if suitable labour can be found in Europe to fill the vacancy — earns at least a gross salary of EUR 33,082 per year,
that the foreign executive who holds a management position earns a gross salary that exceeds EUR 55,193 per year.

I got the same feedback from Deloitte that advised me for better tax situation for expat status. As I doubt that executives earn less when coming here, it worth to apply for expat tax regulations. All you need is a proof that you still have to pay in the country you worked before (insurances, rent, bank accounts, family residence etc)