alt + keys

hai,

1)     while i gave the following command the <alt>+keys disabled.

 gconftool-2 --direct --config-source
xml:readwrite:/etc/gconf/gconf.xml.mandatory --type string --unset
 /apps/metacity/gloobal_keybindings '<Alt>+F3

can u help me how to enable <alt>+keys

2) how to diable backgroud image, screensaver setting to users

3) can u give good link for gconftool-2 with examples

thanks in advance

karthikeyan.N