assuming waveform duration <= 100mS
using a resoloution of 100uS requires 1000 bits (125 bytes) to describe each wave [in a sampled fashion]

easy enough to clockout two independant waves this way but a pic16f876a with only limited(384 bytes i think) ram is a bit tricky

have you thought about other ways to "describe" your wave forms , are they fixed or do they vary . can the be subdivided into fixed and variable sections [header and footer maybe ?]