What it sounds like here is different Tab sizes.

When you say they sometimes work and sometimes don't I am wondering if that is a result of the tab size falling dead on the size needed.

Example :
Code:
Tab Size 8
.......8.......8.......8.......8

One     Two     Three   Four    Five

Tab Size 4
...4...4...4...4...4...4...4...4
One Two Three   FourFive
Notice how it appears that there is no Tab between Four and Five because Four is exactly the number of characters for the Tab?

I am wondering if Win2000 is reading RTF in a different way than Win95/98 and so it is putting the tabs in differently or the base font is different to cause different size text.