Keep your XP machine shut down.
On your WINDOWS 7 machine, issue the command
nbtstat -a [name of the pc]
nbtstat -a WDTVLIVEHUB (assuming you didn’t change its name.)
Post the results of that command here.
Here’s more information:
This is how to find possible problems with the Master Browser on your network, which will affect when and what servers appear on your WDTV Network Shares.
On one of your PCs, open up a “Command” window.
(In Win Vista and Win7, click the Orb, and in the search box, type CMD. An icon will appear above the box that says cmd.exe. Click it, and a Command window will open.)
(In WinXP, Click START, then RUN…, and in the box, type CMD. A Command Window will open.)
In the command window, enter the command “net view,” like this:
Server Name Remark
\BIGNAS1 Big Freakin’ NAS Server 1
\WDTVLIVE WDTV LIVE
The command completed successfully.
In my example, there are four active devices that Windows has discovered.
Now, for EACH of those, issue the command “nbtstat -a (name)” for example:
C:\Users\Tony>nbtstat -a bignas1
Local Area Connection:
Node IpAddress: [10.0.0.157] Scope Id: 
NetBIOS Remote Machine Name Table
Name Type Status
BIGNAS1 <00> UNIQUE Registered
BIGNAS1 <03> UNIQUE Registered
BIGNAS1 <20> UNIQUE Registered
…__MSBROWSE__.<01> GROUP Registered
WORKGROUP <1D> UNIQUE Registered
WORKGROUP <1E> GROUP Registered
WORKGROUP <00> GROUP Registered
So, we got lucky here, the FIRST system, BIGNAS1, indicates that it is the master browser, since it lists the name …__MSBROWSE__.
You need to find out WHICH system is your master browser. If none of these steps work as described, then the issue is likely on your PC itself, and that will require substantial additional troubleshooting.