Here is my two cents worth. I have used Win2k for some 10 years, although that machine hasn't been on the Internet for some three or four years now. I had a rootkit virus once and it was NO FUN! I finally got rid of it using SuperAntiSpyware. You can use it for free and even get support through their forums. I found their response time of 1-2 hours was better than the once a day support I could get through Sophos, a company that only sells AVS to businesses. If you want to pay, it is only $20 or $30. I don't think you can trash your system with it very easily.
I think the threat is real. Win2k no longer gets updates to security problems and when "they" find problems in the newer systems, those problems are likely in Win2k as well. It is pretty easy to deal with this problem. You just have to acknowledge that you have a problem. Maybe you aren't infected with a virus yet... the keyword being *yet*! But why not deal with it now and get that off the table?
Rick