Microsoft doesn't make drivers, whoever made the hardware does. Even the drivers that ship with Windows are not made by Microsoft, they are just bundled with Windows. You cannot expect a company to keep developing drivers for discontinued legacy products.
Windows 7 (and Vista) requires a modern (well, DirectX 9+) 3D card with at least 128MB of memory. It will load Vista and XP graphics drivers if you have them, although with reduced functionality (with XP drivers, severely reduced), but it just shouldn't be installed on hardware that isn't modern and supported. It's an OS for current PCs, not your old A600.