From the SF bug (to keep both places mostly in sync)
"Q: My Computer does not recognize my 42-420 Why?

A: The 42-420 with Windows XP should be recognized as a 'Audio Player'
under 'My Computer' which is a MTP device when using Windows XP and Windows
Media Player 10 or 11 and Vista which has Windows Media Player 11. With
older versions of Windows, or older versions of Windows Media Player, it
will be recognized as a 'Removable Disk' a MSC device instead.

Here are some suggestions for recognition issues.

Please try the USB ports on the back of the PC. If you are using a USB hub
or
ports on the front of the PC, the power draw of the 42-420 could exceed
their capacity and prevent the player from being recognized correctly.

Upgrade your computer with the latest version of Windows Media Player
available for your operating system. Even if you do not plan to use Windows
Media Player with your 42-420, it still requires device drivers that come
with Windows Media Player. You can download the latest version of Windows
Media Player for your system from here:

http://www.microsoft.com/windows/windowsmedia/player/versions.aspx.

Also, please check your Device Manager to make sure it is not a issue with
Windows.

Uninstall the 42-420 via device manager. The 42-420 needs to plugged in to
do this. Go to Start, Control Panel and select 'Performance an
Maintenance'. Then Select 'System'. Then select the 'Hardware Tab' and
select 'Device Manager'. Then find a device called 'Portable Devices' or
'Windows Portable Device'. Then select the + sign next to the device and
right click the 'Audio Player'.

Select 'Uninstall'. Click 'OK' when it asks you if it is OK to uninstall.
Then select 'Action' at the top of the Window and select 'Scan for hardware
changes'. Then once it re-installs the driver, see it operates
correctly.

Also, performing a firmware recovery procedure can work to make your
computer recognize the 42-420. "
http://mymusix.mmvoice.com/products/audio/42-420/faq.html

The firmware recovery procedure is described further down in the FAQ. It
appears as a SigmaTel device:
===
Date: Wed, 17 Dec 2008 15:56:27 -0600
From: Joseph Pingenot <email address hidden>
To: <email address hidden>
Subject: updating the firmware on a SigmaTel-based MP3 player
User-Agent: Mutt/1.5.18 (2008-05-17)

Hello.

I'm a Linux user who got a RadioShack GigaWare MP3 player, which is
apparently a rebranded Perception Digital PD-6140, which apparently
uses SigmaTel chips. I'd like to write a firmware updater, if one
does not already exist, for the Sigmtel chip on this mp3 player.
It appears as
"Dec 17 13:57:11 borkborkbork kernel: [600787.585853] hiddev97hidraw3:
USB HID v1.10 Device [Sigmatel, Inc. ROM Recovery] on usb-0000:00:1a.7-3"
in the system log, with the following lsusb -vv output:

Bus 004 Device 034: ID 066f:3770 SigmaTel, Inc.
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x066f SigmaTel, Inc.
idProduct 0x3770
bcdDevice 0.01
iManufacturer 1
iProduct 2
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 34
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 3
bmAttributes 0x80
(Bus Powered)
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 0 No Subclass
bInterfaceProtocol 0 None
iInterface 4
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.10
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 144
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Thank you very much for all of your help!

sincerely,
Joseph Pingenot
===

Sadly, SigmaTel didn't want to tell me how to help them sell more
hardware. :(