I am getting the following error messages on install - can anyone help?

If you receive a fatal error, refresh this page to continue the installation

Creating 'mysite/_config.php'...
Creating C:\wamp\www\silverstripe/mysite/_config.php
Creating '.htaccess' file...
Creating C:\wamp\www\silverstripe/.htaccess
Building database schema...
Notice: Warning: there are two 'bg_BG' files with the same filename: 'C:/wamp/www/silverstripe/cms/lang/bg_BG.php' and 'C:/wamp/www/silverstripe/auth_openid/lang/bg_BG.php'. This might mean that the wrong code is being used. in C:\wamp\www\silverstripe\sapphire\core\ManifestBuilder.php on line 256

Notice: Warning: there are two 'cs_CZ' files with the same filename: 'C:/wamp/www/silverstripe/cms/lang/cs_CZ.php' and 'C:/wamp/www/silverstripe/auth_openid/lang/cs_CZ.php'. This might mean that the wrong code is being used. in C:\wamp\www\silverstripe\sapphire\core\ManifestBuilder.php on line 256

Notice: Warning: there are two 'da_DK' files with the same filename: 'C:/wamp/www/silverstripe/cms/lang/da_DK.php' and 'C:/wamp/www/silverstripe/auth_openid/lang/da_DK.php'. This might mean that the wrong code is being used. in C:\wamp\www\silverstripe\sapphire\core\ManifestBuilder.php on line 256

...etc

&

Fatal error: Class 'Extension' not found in C:\wamp\www\silverstripe\sapphire\core\model\DataObjectDecorator.php on line 16

I really need to get this installed...