"stop" yes, "resume" no, atleast in that sense
P6 has area render though, so you can get around resume, a bit

1) hit cancel, the currently done render remains

2. copy the pic to a paint program and save
3. save the scene and exit
4. later load scene
5. using area render, render a box slightly larger than the unfinished area
6. copy and composite with the previous pic

i've used this to do network renders before, as poser is quite slow