Websphere Studio Application Developer, Software Updates

My current configuration is:
IBM WebSphere Studio Application Developer (Windows)
Version: 5.1.0
Build id: 20030726_2016
I want to use "Software Updates" to install the latest
and greatest WSAD enhancements and fixes.
I am using WSAD from my company's intranet.
I enabled the HTTP Proxy and provided a username and password
for the Proxy authentication.
The Software Update does not work for me.
This is what I observe:
Help --> Software Updates --> New Updates
Progress dialog "Searching for updates"
Network connection problems encountered during search.
Unable to access "http://www3.software.ibm.com/ibmdl/pub/software/websphere/studiotools/wsad51/update".
Unable to access Site stream: "http://www3.software.ibm.com/ibmdl/pub/software/websphere/studiotools/wsad51/update" [http://www3.software.ibm.com/ibmdl/pub/software/websphere/studiotools/wsad51/update]
Cheers,
-Sean

I found this note in the WSAD 5.1.0 README file:
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1.3 Accessing update sites through a proxy
To access an update site through a proxy, you will need to start the workbench with the following command line options:
wsappdev.exe -vmargs -DproxySet=true -DproxyHost=<proxy_name> -DproxyPort=<proxy_port>
Proxies requiring user authentication are currently not supported.
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