Citrix have released a new version of Online Plug-in for windows that support IE9.
This plug-in is supported on Windows 7, XP, Vista, 2003, & 2008.
Use the Citrix Online plug-in to access your hosted applications or virtual desktop.
This hotfix adds support for launching applications from the Web Interface using Windows Internet Explorer 9. With earlier versions of the plug-in,
attempts to launch applications from the Web Interface using Windows Internet Explorer 9 fail with a sharing violation. If you are not affected by this issue
in your organization, there is no benefit to installing this hotfix.