Summary form only given. Recently, photonic crystal fibers have attracted considerable interest for their unique structure and optical properties. These fibers contain an ordered array of air holes which form a low-index cladding around a solid silica core. Other examples include fibers with hollow cores where light is guided by a photonic bandgap effect. Understanding the propagation of fs pulses in these fibers, and in particular the origin of nonlinear effects such as continuum generation, is important for optimizing their applications. In our experiments, we employ a 95 cm segment of fiber having a 2.5 micron silica core suspended in air by a web of sub-micron silica strand with a cladding diameter of 90 microns. 170 fs pulses from an optical parametric oscillator at a wavelength of 1550 nm of variable average power are coupled into the fiber. The output from the fiber is then analyzed spectrally and temporally and the fundamental pulses are sent to a frequency-resolved optical gating apparatus.