How to remove win2000 on current pc and

I have windows 2000 on a pc and all works fine except the Lotus notes ver 4.61. I have tried many many times to get it going, but once I put Notes on the win2000 pc and try to open notes it freezes forever and I end up rebooting and get no where. So, I have to remove the windows 2000 and install windows NT. Can anyone give me a foolproof procedure to follow to install the windows nt in place of the windows 2000.
Thank you, thank you ,for any help offered.
ps..I also tried installing LOtus Notes ver 5..not luck there either.
Claudette