  We show how to divide a coupled multi-spin system into a small subset of
``active'' spins that evolve under chemical shift or scalar coupling operators,
and a larger subset of ``spectator'' spins which are returned to their initial
states, as if their motion had been temporarily frozen. This allows us to
implement basic one-qubit and two-qubit operations from which general
operations on $N$-qubits can be constructed, suitable for quantum computation.
The principles are illustrated by experiments on the three coupled protons of
2,3-dibromopropanoic acid, but the method is applicable to any spin-1/2 nuclei
and to systems containing arbitrary numbers of coupled spins.
