Which operating systems are supported... depends on which web browser you are using. 

The Internet Explorer version only works with Windows 2000, all flavors of Windows XP (including Home, Pro, Media Center Editions, and Server 2003), and all flavors of Windows Vista.  With Internet Explorer, Windows 9.x (W95, W98, W98se, WME) is not supported.

Firefox can use the toolbar on any OS capable of running Firefox.  This includes Windows 9.x (W95, W98, W98se, WME), Windows 2000; all flavors of Windows XP (including Home, Pro, Media Center Editions, and Server 2003); all flavors of Windows Vista; various distributions of Linux; and Macintosh OS X.

Certain features, such as the streaming radio, only work with Windows and/or those browsers & operating systems that support (either natively or via add-ons, extensions, etc.) Windows Media Player, ActiveX, and .asx streaming.

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