If it suits your needs then there's no point in changing is there? I have moved to 2007, and I find the interface much more user friendly, but that's personal preference.
You can get hold of a trial version of 2007 so why not download it, install it alongside 2000 and then remove it if it doesn't suit.
One good reason you may want to consider for moving to 2007 is the MS don't support their products forever and mainstream support for 2000 ended in 2004 and extended support is due to end in 2009, after which you will no longer get security updates for it. So you still have a couple of years to make your mind up :-)