RemoveWAT (Windows Activation Technologies) is a well-known third-party utility used to bypass the activation requirements of Windows operating systems, including Windows Vista Home Basic (32-bit).
Extend the Trial Period (Rearm): Windows Vista allows you to extend the 30-day activation grace period legally using the "rearm" command. You can do this up to three times for a total of 120 days.
Security Risks: Tools like RemoveWAT are often distributed through untrusted third-party sites and may contain malware or viruses.
The watermark you're referring to is likely the "Activate Windows" or "Windows Vista Home Basic" watermark that appears on the desktop when Windows is not activated or when the activation period has expired. This watermark can be quite annoying, especially if you're using your computer for important tasks.
System Stability: These tools can introduce software that degrades system performance or prevents official security software, like Microsoft Security Essentials, from running. Legal Ways to Activate or Use Windows Vista
Alternatives to RemoveWat