Beth,
I would generally recommend that people move towards the 2000 environment. For one thing, it adds plug-and-play features, which are not present with NT. It is a slightly bigger resource hog, however, and requires more robust hardware. The learning curve going from NT is not that bad either, which is a concern for some.
Cases can be made to go either NT or 2000, so I guess every situation needs to be evaluated.
Not knowing specifically what your usage requirements are, I cannot make a broad statement to go either way. For example, certain games, and older software may not work on either NT or 2000.
I would truly recommend making an "image" of your hard drive first, using either Ghost, or Drive Image, in case your migration to a new OS does not work out as you anticipated. Then, you can always restore back to the way it was before.
I for one, have learned the hard way in the past, and won't make the same mistakes again.