  We describe a data reduction pipeline for VLBI astrometric observations of
pulsars, implemented using the ParselTongue AIPS interface. The pipeline
performs calibration (including ionosphere modeling), phase referencing with
proper accounting of reference source structure, amplitude corrections for
pulsar scintillation, and position fitting to yield the position, proper motion
and parallax. The optimal data weighting scheme to minimize the total error
budget of a parallax fit, and how this scheme varies with pulsar parameters
such as flux density, is also investigated. The robustness of the techniques
employed are demonstrated with the presentation of the first results from a two
year astrometry program using the Australian Long Baseline Array (LBA). The
parallax of PSR J1559-4438 is determined to be 0.384 +- 0.081 mas (1 sigma),
resulting in a distance estimate of 2600 pc which is consistent with earlier DM
and HI absorption estimates.
