what to do after messing up gnome settings

If you mess up gnome display settings, there might be a situation where gnome does not load. It might log in and then hang. In such a situation, all you have to do to get the default settings back is to delete the configuration files in your home folder.
Log into KDE or start a virtual terminal (CTRL+ALT+F1), and delete the folders .gconf, .gconfd, .gnome2, .gnome2_private. (try rm -rf from terminal)
This will remove all settings and you'll be back to the day when you logged in the first time.

Note: this does not resolve hardware issues!

updating synaptic after first update

On updating karmic for the first time, the package list in synaptic might not be updated. To update the list, run this code.
sudo apt-get update
This will add all the packages like vlc, thunderbird etc in synaptic.