On the machine where DBXL is being installed, there's an Administrator group. That's the BUILTIN\Administrators that gets used by DBXL. So if you're an administrator on the machine, then you'll be a DBXL administrator by default.
Because the databases are getting created, it seems the SQL part of the installation completes successfully. What might be failing is the DAT activation. Which would explain why you can't access DAT. To setup DAT manually, follow these steps (on the server):
1. (If on Windows Vista or Windows Server 2008, run Internet Explorer as Administrator.)
2. Open the following URL in IE: http://<servername>/QdabraWebService/DbxlAdmin.asmx
3. Click on PublishDATFormTemplate method.
4. Enter the path of the DAT-Template form, which is saved to the local drive. In a non-SharePoint default installation, the path will be C:\Inetpub\wwwroot\QdabraWebService\install\DATtemplate. xsn.
5. Call PublishDATFormTemplate method by clicking on Invoke button. If you have already created Document Types, you must execute two additional steps after calling PublishDATFormTemplate.
6. Open DAT.
7. Click Edit and Save for all your DocTypes.
Which OS are you using, by the way?