setting up beryl

[cj]

hi all

im trying to set up beryl on my system..

first of all, i installed it using apt-get install beryl

so now that its installed, i open the console and type "beryl" heres 
what it gives me:
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**************************************************************
* Beryl system compatiblity check                            *
**************************************************************

Detected xserver                                : AIGLX

Checking Display :0.0 ...

Checking for XComposite extension               : failed

No composite extension
beryl: No composite extension
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what is the composite extension and how do i fix this problem?
--cj