It's not a question of "working", but a question of security.
But, as time goes on, also "working" will become a problem as more and more software will not run on Win2000.
I am very happy with Win7 though. It is a really good piece of software, and it is not that expensive. The home premium has everything you need as a standard user.
Ubuntu is great, but as you said: if you rely on a certain software that is only available for Windows, it is not the final solution.