WoW, being in IT I expected a slightly better description of the problem and a way to recreate it. "I was directed to download a plug-in". What page were you directed to? What plug-in? Narrow down which page gave you the warning. i.e. go only to the forum. then close the browser, go only to download the plug-in.
FYI, sites don't "get a virus". They get hit with a SQL injection exploit, which then remotely includes code that contains a trojan. 99 times out of 100, there's never a trojan on the site.
I'm not running either Windows or IE, so I'm going to need a little help here. I did search through the html output of the site, and didn't see anything being included.