Sudo != root. Sudo is with respect to the user, not the "root" account.

Most of the stuff you do as a user that would normally require "root" rights, like the app manager, are actually using Sudo. Sudo grants the *user* temporary root rights to run the applications.

Sudo has been configured to grant user the right to be root with specific commands *without a password*. Meaning that if you set a root or user password it won't matter because sudo has been told "don't ask".

The way Ubuntu does it, is it has two wrapper programs: gksu and gksudo. Your user account has a password that only you are supposed to know, when you launch Synaptic or whatever package manager *that* sudo has been told "Ask for a Password" and it uses gksudo/su to prompt a GUI password box for you to put that into.

AFAIK: No gui password prompt program is available for the N900 and thus that specific solution would require manual work in making one. The other possibility is you set yourself a user password (leave root locked unless you have specific reason to need it), and then completely change your sudoers file to prompt for a password in order to gain root.

However, you would then need to go through and modify every .desktop file and have it launch in a terminal window instead of directly so that your terminal will ask for the password. Not elegant, and certainly not easy... not to mention extremely likely to brick the device unless you know exactly what you're doing.