Your location should be "Microsoft.SharePoint.Administration.ApplicationManagement" and GroupID should be SiteManagement.

The values you use for Location and GroupID must match with what is documented here: http://msdn.microsoft.com/en-us/library/bb802730.aspx

I realize that Location and GroupID attributes mentioned in SDk are not correct: http://msdn.microsoft.com/en-us/library/bb802730.aspx

The values you specified are correct.

I was able to display a link with following XML, which is pretty similar to yours:

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <CustomAction  GroupId="SiteCollections" Id="CheckAllaboutmoss" Sequence="100" Location="Microsoft.SharePoint.Administration.Applications" Title="Check Availability" RequiredAdmin="Delegated" >
    <UrlAction Url="/_admin/createsite.aspx"/>
  </CustomAction>
</Elements>

**Please make sure following:

1. You can use Scope = Web or higher (Web makes sense)
2. Make sure you have AutoActivateInCentralAdmin="TRUE" in the FEATURE element of the feature.**