You forgot Mimer
If I have to choose between MsSQL and Oracle, I would choose Mimer
Mimer is probably the most standards compilant database available. It is also very easy to set up and aministrate.
Mimer is unfortunately not OSS...
It sounds like you're talking about GConf (http://freshmeat.net/projects/gconf/).
GConf stores configuration using a backend of choice (currently implemented backends are xml and db). You access all values
using paths like "/apps/galeon/UI/Tabs/tabbed_loading_color". Aplications are informed when a value changes.
I don't know if it is secure enogh to be used for serverprogramming.