star formation (e.g. Shu, Adams, & Lizano 1987), the first evolutionary phase in the path from molecular cloud to main sequence star involves the formation of gravitationally-bound, starless dense cores (e.g. Myers 1999). These “pre-protostellar” (or “pre-stellar” for brevity) cores (cf. Ward-Thompson et al. 1994) are thought to be initially supported against their self-gravity by magnetic and/or turbulent pressure, and to progressively evolve toward higher degrees of central concentration through ambipolar diffusion (e.g. Mouschovias 1991) and/or the dissipation of turbulence (e.g. Nakano 1998). At some not yet well understood point, the cores become unstable and collapse dynamically to form accreting protostars which quickly become detectable in the radio range as Class 0 objects (André, Ward-Thompson, & Barsony 1993) and subsequently in the infrared as Class I sources (eg. Lada 1987). Additional complications arise in regions of multiple star formation (such as the $\rho$ Ophiuchi central cloud) where external triggers rather than self-initiated ambipolar diffusion may be responsible for cloud fragmentation and core formation (e.g. Loren & Wootten 1986; Boss 1995; Whitworth et al. 1996; Motte, André, & Neri 1998 – hereafter MAN98).

A good knowledge of the initial conditions for rapid protostellar collapse in star-forming cores is crucial to get 