Well I Posted a similar block recently with the ability to let users internal search your moodle site.
it uses Google as this one but also msn and yahoo at your preference.
Since there was any feedback(anyone tried it on 1.6?) it that i post here for everyone to choose and see more as a choise .
http://moodle.org/mod/forum/discuss.php?d=40636
Thanks
Blocks
Simple Google Search Block for 1.5
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