To use the vmdk file, open VMware and...

To use the vmdk file, open VMware and create a new virtual machine. One of the options will be to use an "existing virtual disk."

This statement is wrong. This option doesn't exist. 

This is how I got it to work with the image that Gdgt is providing and the VMWare Player currently available for free download from VMWare's site...

1) Create a folder on your C drive called Virtual Machines

2) Download the Chromium image from Gdgt and extract the VMDK file to c:\Virtual Machines

3) Download and Install VMWare Player

4) In VMWare Player...
a. Select "Create a New Virtual Machine"
b. Select "I will install the operating system later" and click the Next button
c. Under Guest Operating System select Other and under Version select Other and click the Next button
d. Under Virtual Machine Name enter "Chrome OS" and under Location browse to the c:\Virtual Machines folder you created above and click the Next button. [Note: This will be the downloaded VMDK file and the newly created blank Virtual Machine in the same folder]
e. On the Specify Disk Capacity page leave defaults as they are and click the Next button.
f. On the Ready to Create Virtual Machine page click the Finish button.

5) Navigate to the c:\Virtual Machines folder in Windows Explorer.
a. Rename Chrome OS.vmdk to Chrome OS.vmdk.old
b. Rename chrome-os-0.4.22.8-gdgt.vmdk to Chrome OS.vmdk

6) On the VMWare Player main screen select Chrome OS and click Play Virtual Machine [Note: This will show the OS logon screen]

7) In the bottom right hand corner of the VMWare Player window right click on the Network Adapter Icon and click Disconnect then select Settings.

8) On the Virtual Machine Settings window on the right hand side under Network connection select Bridged and then click the OK button.

9) In the bottom right hand corner of the VMWare Player window right click on the Network Adapter Icon and click Connect

10) On the OS logon screen enter your Google e-mail address as your username and your Google password as your password.