HTC Sync only works via the USB cable. You will not be able to read your PC's files from your phone via HTC Sync like you would with Window's Explorer.
To access your PC from your phone via wifi you need to install an app like ASTRO Manager (plus ASTRO SMB Module) or ES File Explorer.
To set up your PC to work with either of these apps or similar, you'll need to know your router/PC IP address and enable your PC to share its files, i.e. allow another computer (your phone) read/write access to your PC.