Right-click on the db/textworks installer. Choose "run as administrator". You may be prompted to proceed and/or enter administrative credentials, depending on your Vista setup. The installer will start installing and should work fine.
If you do not run as administrator, you will get an error like this:
Error 1925. You do not have sufficient privileges to complete this installation for all users of the machine. Log on as administrator & retry installation.
You may be confused by this message if you are logged in as an administrator. Welcome to Vista's User Account Control (UAC).
With UAC, you may have logged in as an admin, but you are not running as one. Instead you are prompted to elevate your permissions whenever you attempt an administrator-level operation. It so happens that Inmagic has not updated db/textworks to handle this scenario and give you fair warning. The error message it gives upon failure is at least completely accurate in its diagnosis, but leaves it up to you to manually elevate your permissions.
Here are some other Inmagic-on-Vista related posts on the Andornot Developer Blog: