So far as I know, the rule was always "don't bother buying any MS software until version 3".<p>MS-DOS: v1.0, v2.0, v3.3<p>Windows: v1.0, v2.0, v3.0<p>Windows NT: v3.1, v3.51, v4.0<p>Word for Windows: v1.0, v2.0, v6.0<p>Visual Basic: v1.0, v2.0, v3.0<p>There's probably other examples, but I'm not sufficiently familiar with Microsoft's other (or newer) products to list them.