Difference of VBA in Word 2000 and Word xp

Hi,

I have a .net application in C# that intracts with microsoft word. Previously it was designed for win xp and office xp. Now I would like this to work on Win 2000 and office 2000. But it is giving some problem.

I looked into the code and could figure it out that some functions are giving exceptions. Following are examples.

1. Document.SaveAs method works in Word XP but not in Word 2000. However Document.SaveAs2000 works in Word 2000.

2. Range.PasteAndFormat works for Word XP but not for Word 2000. However Range.Paste() works in Word 2000.

Is there any reason behind this. Is it somewhare mentioned in Microsoft website?? Could you please get me some link where this information is mentioned.

Are there some other functions that behaves similar to above mentioned?

Thanks in advance.
Ashish