Looks like a failed Java Plugin installation.
I checked
http://java.sun.com/j2se/1.4.2/install-windows.html and it says this:
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When installing version 1.4.2 of Java 2 Runtime Environment or Java 2 SDK (using the default minimized download rather than the single executable), InstallShield requires Microsoft Windows Installer 2.0 to be on your machine; if it is not found (or an older version is found), then InstallShield automatically tries to download Microsoft Windows Installer 2.0. If your machine is not on the Internet or is behind an authenticated proxy, the installation will fail at that point.
To proceed, simply use the Windows Offline Installer from the download page. Microsoft Windows Installer 2.0 is included in this download.
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So then, I would UNINSTALL the Java 2 Runtime Environment again, reboot, and do one of the following:
Get the Windows OFFLINE installer - use the Download J2SE v 1.4.2_02 (the link for Standard Edition 1.4.2_02 ) from
http://java.sun.com/j2se/1.4.2/download.html - be sure to click the JRE link, not the SDK - it will eventually take you to a page that says:
You have chosen to download Java(TM) 2 Runtime Environment, Standard Edition 1.4.2_02
* Download j2re-1_4_2_02-windows-i586-p.exe .
Filesize = 15,224,368 bytes.
Save the download to your desktop or other easy to find location. Exit your browser when the download is complete and close all running programs, and be sure to disable your antivirus program before running the j2re-1_4_2_02-windows-i586-p.exe file.
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Get the earlier version 1.4.0_01, which I KNOW works with Yahoo Games (it's the version I use) and I KNOW it doesn't need the Windows Installer Package. Get it here:
http://java.sun.com/products/archive/j2 ... index.html
Also download the file, close the browser, etc. and install with your antivirus disabled.
Good luck.
P.S. you said that
The website said that my computer was running on an unknown platform
You haven't spoofed your useragent, have you?
See
http://plugindoc.mozdev.org/faqs/java.html
"Known Issues"
UserAgent: Mozilla/5.0 (Windows; U; Win95; en-US; rv:1.5) Gecko/20031007