PA Server Monitor can associate a set of Windows credentials with a monitored computer.
The following context menu let you access the Set Windows Credentials dialog. If you don't see the SSH menu, you need to set the Server Type.
You can enter credentials, or just monitor the server using the login that the monitoring service is already using. The middle radio button is a convenience feature -- it lets the system try already-entered passwords to find one that works.
When you press OK, the credentials are checked by trying to access the target server's Event Log and the list of running services. If this succeeds, the credentials are saved.
The help page Remote Monitoring Hints has some advice and information about user accounts when monitoring Windows servers.
All credentials are protected using the Microsoft best practice of encrypting them with a machine-specific key, which means they can only be decrypted on the same computer they were encrypted on.