  We study the energy propagation in subwavelength waveguides and demonstrate
that the mechanism of material gain, previously suggested for loss
compensation, is also a powerful tool to manipulate dispersion and propagation
characteristics of electromagnetic pulses at the nanoscale. We show
theoretically that the group velocity in lossy nano-waveguides can be
controlled from slow to superluminal values by the material gain and waveguide
geometry and develop an analytical description of the relevant physics. We
utilize the developed formalism to show that gain-assisted dispersion
management can be used to control the transition between ``photonic-funnel''
and ``photonic-compressor'' regimes in tapered nano-waveguides. The phenomenon
of strong modulation of group velocity in subwavelength structures can be
realized in waveguides with different geometries, and is present for both
volume and surface-modes.
