SD 2.1.4 on OS 10.3.9... working?
 

I am attempting to back up my hard drive to a disk image over a FireWire 800 connection. So far, it has been running for 1h 30m and is still on the "Preparing [Hard Drive]" stage. The clock is running and the cursor is spinning, but nothing seems to be happening. Anything I can do?

Stop it and restart your Mac (and power cycle your drive): it sounds to me like your drive isn't responding properly.