Sony Walkman can be used as an external hardware using the USB mode. This mode is very helpful for syncing and transferring files from a computer. However, people using Napster may face an issue with this mode and would be required to switch from USB to MTP mode. To get around this problem one should connect Sony Walkman to the PC and find the device under USB controllers via Device Manager. One should uninstall the device and plug in the device again. The device should have successfully switched from USB to MTP mode.
This fix changed my Sony Walkman to a USB devce. This solved the problem with WMP (I could now sync and transfer files via drag and drop).
However, now tracks that I have downloaded with my Napster to Go subscription do not work as (I think) the device is showing up as a USB device rather than an MTP device. I tried performing the opposite of the steps above but Vista keeps on opening it up as a USB device.
In the properties for the portable device, the drivers are listed as:
The driver software is shown as:
Microsoft WPD FileSystem Volume Driver.
Connect the device to your PC
In device manager look under 'Universal Seral Bus controllers', you should have one listed with the name of your walkman.
Right-click it and uninstall. Re-plug in your walkman and it should be back to normal.