"Standard" NetApp OS (ONTAP 7G) supports clustering of two nodes only.
They both have to be active in that sense they need to be running & both need some disks associated with them. You have the choice though to either split the disk ownership more or less evenly between two nodes (true a/a) or assign only 3 disks to one node (to keep its root volume there) & all the rest to another node (effectively a/p setup).
ONTAP GX, which does multi-node clustering, doesn't support 2000 series boxes. I am not sure whether it is going to change with the introduction of ONTAP 8, which in essence will (sort of) merge GX & G versions of ONTAP.
Regrads,
Radek