Complex sentence: Impelled by flattening Macintosh sales around 1995, Dantz started expanding into the Windows market; by 2001 as many copies of Retrospect for Windows were being sold as copies of Retrospect for Macintosh.
Split into simpler sentences: Impelled by flattening Macintosh sales around 1995, Dantz started expanding into the Windows market. By 2001 as many copies of Retrospect for Windows were being sold as copies of Retrospect for Macintosh.