Hi Liggy,
I am yet another user who has a Dell 6000D with an NEC ND-6650 dvd +/- rw drive with the OEM 102c firmware.
I am simply looking for the bitset functionality for DVD+R media.
In my case, I have found this to be most compatible combination for my DVD players. I have been using this combination with great luck with my Dell 8400 Philips DVD+-RW DVD8631.
Based on what I have read on these forums:
1) I have purchased a slimline IDE adapter
2) I am hesitant to use your existing 1.23 or 2.23 firmware since it is "older" than the 102c firmware I currently have.
Liggy 1.23 and 2.23 Firmware
In addition, there seems to be some updated NEC ND-6650 firmware, NEC 1.42 which seems to be at the same version level as the Dell OEM 102c firmware.
NEC-6650A Original Firmware
Firmware Release Date Version BitSetting
dd/mm/yy CD-R CD-RW DVD-R DVD-RW DVD+R DVD+RW DVD+R9 DVD-R9 DVD+R DVD+R9 DVD+RW
NEC 1.23 20/04/2005 1.12 1.13 1.12 1.16 1.19 1.17 1.07 1.03 No Yes No
NEC 1.23 (Liggy) 20/04/2005 1.12 1.13 1.12 1.16 1.19 1.17 1.07 1.03 Yes Yes Yes
NEC 2.23 (Liggy) 20/04/2005 1.12 1.13 1.12 1.16 1.19 1.17 1.07 1.03 Yes Yes Yes
NEC 102C 24/06/2005 1.15 1.14 1.13 1.18 1.19 1.17 1.07 1.03 No Yes No
NEC 1.42 09/06/2005 1.15 1.14 1.13 1.18 1.19 1.17 1.07 1.03 No Yes No
What would you suggest?
You are the master 
Thanks,
BL