Hi Don,
The Latitude D800 is factory installed with PC2100 (266 MHz) memory. PC2700 (333MHz) memory is also compatible, but if installed, it will only run at a 266 MHz bus speed.
You have mentioned in the post that you are getting a blue screen with the new memory. Please check if you are getting any error message and let me know the exact error message.
Also run diagnostics on the hardware components of the system. To run diagnostics restart the system and at the Dell logo tap the F12 key every two seconds. This will start the One-time boot menu. Using arrow keys select ‘Diagnostics’ and hit enter. This will run diagnostics on the hardware components of the system which may take around 5 minutes. Please reply to this post in case of any error message.