I finally had the chance to try again yesterday. Finally got it to work by a) using a SATA port on a different controller - it turns out the last two on my motherboard proper are malfunctioning; b) doing manual editing in Hex Workshop while in a good SATA port; c) running HDDHackr again, from the top - flashing drive, modifying IntelliPark, and creating the partitions.
One thing I noticed was that simply pressing enter at the prompts in HDDHackr doesn't auto-fill them with a default valud for your filenames, like HDDSS.bin. You have to actually type this and any other file name in. Or else it WILL give you a checksum error. That I was still getting this even after switching to a working SATA port drove me nuts!
Another thing is that once the partitions are created, the program doesn't exit after saying that it has successfully created the partitions. At that point, it is safe to shut off your PC.
Thanks again to InsaneNutter for this guide...$50 in my pocket