Yes, you will be free to travel in the Schengen Area using your national "D" type visa.
Legal basis:
Regulation EU No 265/2010 of the European Parliament and of the Council amending
the Convention Implementing the Schengen Agreement and Regulation (EC) No
562/2006 as regards movement of persons with a long-stay visa
The Regulation enters into force on 5 April 2010, which means that
from that date All valid long-stay visas will allow for free
circulation in the Schengen area for three months in a six
month-period. A third-country national holding a long-stay D visa
issued by a Member State will be allowed to travel to the other Member
States for three months in any half year, under the same conditions as
the holder of a residence permit. In accordance with the Regulation,
this rule also applies to long-stay visas already issued before 5
April 2010, including still valid D+C visas;
and from the Regulation itself (the Regulation amends Convention Implementing the Schengen Agreement, therefore Article references apply to the Convention):
Article 21:
‘1. Aliens who hold valid residence permits issued by one of the
Member States may, on the basis of that permit and a valid travel
document, move freely for up to three months in any six-month period
within the territories of the other Member States, provided that they
fulfil the entry conditions referred to in Article 5(1)(a), (c) and
(e) of Regulation (EC) No 562/2006 of the European Parliament and of
the Council of 15 March 2006 establishing a Community Code on the
rules governing the movement of persons across borders (Schengen
Borders Code) (*) and are not on the national list of alerts of the
Member State concerned.
[...]
2a. The right of free movement laid down in paragraph 1 shall also apply
to aliens who hold a valid long-stay visa issued by one of the Member
States as provided for in Article 18.’.
Article 18:
- Visas for stays exceeding three months (long-stay visas) shall be national visas issued by one of the Member States in accordance with
its national law or Union law. Such visas shall be issued in the
uniform format for visas as set out in Council Regulation (EC) No
1683/95 (*) with the heading specifying the type of visa with the
letter “D”. They shall be filled out in accordance with the relevant
provisions of Annex VII to Regulation (EC) No 810/2009 of the European
Parliament and of the Council of 13 July 2009 establishing a Community
Code on Visas (Visa Code) (**).
Source:
- http://www.sztokholm.msz.gov.pl/resource/22c47820-a6ec-4d81-9601-a7211e2316c4:JCR (information note from Polish Embassy in Stockholm)
- http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2010:085:0001:0004:EN:PDF