My experience is that most of my old xl95 & xl97 code runs in xl2000 fine, as they use the hidden objects, properties, methods. However writing new code in xl2000 requires a lot of care if writing for backward compatability. Most code is 'ambidextris' but there are a lot of commonly used methods & properties that, although documented as working the same, do not. xl97 has a lot of 'teething' problems I guess 'cos it was the first to use the common MSOffice VBA engine.
These are some of the topics copied directly from xl2000 help.
Hidden Objects
Hidden Properties and Methods
Language-Specific Properties, Methods, and Functions
Methods with New, Changed, or Deleted Arguments
New Events
New Methods (Alphabetic List)
New Methods (by Object)
New Objects
New Properties (Alphabetic List)
New Properties (by Object)