OK... After long long hours of searching and losing hope, I think I'm the first person to ever fix this. Here is what I did;
-- using xplorer360 extreme 2, I created a hddss.bin file, but it didn't work by itself when restored. I also backed up the gamer profile folders in Partition 3 > Content
-- I followed the directions here ---> http://www.xboxhacker.net/index.php?topic=12062.0;wap2
to wipe my 20GB Hitachi HTS541020G9SA00 clean.
-- After those steps I used hddhackr with the command "hddhackr c FD00(address of drive may differ) A00" to create the 0,2, and 3 partitions.
-- I downloaded various hddss.bin for 20GB HItachi hard drives, but looking in WinHex, none of them were the same model as my drive.
-- After restoring every 20GB hddss.bin image I could get my hands on, none of them made my 20GB Hitachi HDD recognizable inside of my xbox 360. The original hddss.bin obviously didn't work, either, since it was made while the hdd was having problems.
SO! Here's where the important bit comes in!!!
-- First, I wiped the hard drive clean for the 10th time (UGH!), and partitioned it using HDDHACKR.
-- I then opened my old hddss.bin backup using WinHex and went to Position > Go To Offset and type "2000" and selected the blocks from 00002000 to 00002CC0 (my theory is that this is the important drive model and firmware information) then went to Edit > Copy Block > Normally
-- Next, I opened the downloaded Hitachi 20GB HDDSS.BIN (not from the same model of Hitachi drive) and placed my cursor at the very first block of 00000000, and clicked Edit > Clipboard Data > Write
--Now I have a hybrid HDDSS.BIN image file.
-- I then clicked File > Restore Image, selected the hybrid hddss.bin file, then selected the physical drive (Hitachi HTS541020G9SA00), with the options "Simultaneous I/O" and "Copy Entire Medium" selected, and in the box "Start Sector (Destination)" I entered "16".
-- After restoring the image I put the hard drive into the xbox 360 and BAM! It recognized it!!! I formatted using the console option, then hooked it back up to my PC and restored the game profile folders and now everything is 100%!
I really hope this helps somebody else that had given up on their drive! Contact me if you need the hddss.bin for a Hitachi 20GB HTS541020G9SA00 hard drive!