teil - checkout luberths site. he has several mentions of raster to vector
i have had decent results with macromedia flash! it is free for 30 days, and totally a great program, just hard to learn.
adobe streamline produces a decent program - but it feels sort of old and limited? i used it untill i found out how much better the flash one is.. but i use them for artwork, not cnc.
there are several cnc controller programs that load raster. mach1\2, deskcnc, etc. i think.
there is something called "bmp2gcode" that got mentioned in one of the gantry painter threads, as well as some other sofware.
www.majosoft.com might also have one. there are many many of these.
what is your specific use? i use the flash convertor to change handdone sketches into vector art without tracing, i also use it to make simple 3d images much smaller for websites. there is a bunch of it on my personal website: www.vacuumstudios.com/rg.html