Microsoft does not offer Visual Studio 6.0 for free. Unlike some older versions of Windows or Office, VS6 was never made available as a free download. The only legal ways to obtain it are:
Microsoft stopped supporting VS6 in 2008. While they allowed existing customers to use their keys forever, Microsoft no longer sells or distributes VS6. This has created a grey market for ISO files and keygens. Microsoft Visual Studio 6.0 ISO With Key
A more compact set, often found as a two-disc MSDN ISO set from 1999. Key Information: Historically, generic keys like 111-1111111 Microsoft does not offer Visual Studio 6
Includes multiple discs for Visual Basic, C++, and the MSDN Library. Professional Edition: and the MSDN Library. Professional Edition: