Should I upgrade to 2000 or XP?

I am an IT Manager of a small network of 30 users. Our servers are running NT 4.0 SP6a-Post and our desktops are running either NT 4.0 or Win 98. Microsoft has notified the public of stopping support of NT 4.0 and Win 98 as of July 31, 2002. My concern is that no support, there would be no enhancements or patches for the operating systems that we currently use. I’m getting conflicting answers from two different consulting companies. One saying that we should upgrade and keep current with our OS and the other saying that if it isn’t broke don’t fix it. I’m curious as to anyone else’s opinion out there. Thanks for you response.