In reply to Anne.

64-bit SAS requires 64-bit Windows. But 32-bit SAS can run on 32-bit Windows OR 64-bit Windows. If you have SAS programs that rely on import/export from Excel, or you have established FORMAT libraries that you share, the 32-bit version might offer you better compatibility. See more information in this post.

Note that SAS currently supports Windows 8 for only a few products.