The step-by-step guide below demonstrates how to connect to your NAS via WebDAV on Mac OS X.
Client Operating System: Mac OS X Snow Leopard (10.6.1)
QNAP NAS Firmware Version: 3.2.0
Open "Finder" > "Connect to Server", and enter the URL of the share folder.
Enter the user name and its password which has the WebDAV privilege to access this share folder.
That's it. Now you can easily access the share folder through this link via HTTP/WebDAV.
You can also find the mountpoint in the "SHARED" category in Finder and make it as one of the login items.
Please note that this instruction is based on Mac OS X 10.6, and can be applied to 10.4 or later.