Do you meet the system requirements mentioned on the Windows 2000 box? If you do then you will be able to install 2000.
The thing is here though, I run Windows 2000 Professional and I was able to buy and install an upgrade version without having NT. I have never owned a copy of that.
I had to buy a full copy of Windows 2000 server but I don't think you need NT to install an upgrade of Professional. I might be wrong though. Can anyone clarify?