  A suitable splitting of tachyon field equation is able to disclose non
trivial properties of Born-Infeld (some known, some unexpected) and Polyakov
actions; the tachyon equation also can be analyzed in some detail. The analysis
displays an intriguing connection between sine-Gordon theory and some crucial
issues such as the emergence of perturbative string states when a D-Brane and
an anti-D-Brane annihilate and the confinement of charged D-Branes.
