If you are a purist who owns the 2002 CD, Windows 7 represents the last Microsoft OS that can natively (with a no-CD patch) run the untouched original PC port—complete with CD audio, pre-license-expiry branding, and no Steam overlay.
If you are a pragmatist, the Steam version + soundtrack mod + dgVoodoo2 runs perfectly on Windows 7 and is the easiest legal route.
Introduction: The Fare That Refused to Die