From 1 May 2006 onwards, a citizen of a EU or EEA member state or
Switzerland who wishes to stay in the Netherlands for more than
3 months, has to register with the Immigration and
Naturalisation Service (IND) after three months, or sooner. This new
procedure does not apply yet (till probably Dec. 2006) to citizens from new member states.

New EU member states
For people from Poland,
the Czech Republic, Estonia, Latvia, Lithuania, Hungary, Slovenia and
Slovakia, the application procedure will remain the same.
They must submit a request for verification against EU Community Law to
their municipal authorities, and will then be given a registration
sticker with a note relating to permission to access the job market. This situation will, in all probability, continue until 31 December, 2006.
After this time, open access to the job market will be available for
citizens of these countries. They will then only have to register with
the IND.

Entitlement to permanent residence
Nationals of
these countries who have resided lawfully in the Netherlands for five
years without a break are automatically entitled to permanent residence
status. They may obtain documentary proof of this status in the form of
a permanent residence card.

The free movement of persons
The Government has
introduced the new rules to implement the European directive on the
free movement and residence of EU citizens and their family members in
the member states.

Read more on a site of IND (in English) or press release of Dutch ministry of Justice (in Dutch) and RVD