Windows NT/2000 contains a boot manager that will allow you to select between windows NT/2000 and other versions of DOS/windows. If you install the DOS/windows operating system first then you can install both this and Windows NT/2000 in the same C: drive and use this boot manager to select between them.
Linux also comes with a boot manager called LILO (some versions also come with more advanced alternatives). When you install Linux after the other two operating systems you can configure this so that you can either select 'windows' to start the NT boot manager to then further select which one or alternatively you can install windows NT/2000 and DOS/windows in separate C: drives (you can have up to 4 primary partitions and choose which one the system can see) you can select between all three from LILO.
You make want to get a third party utility (eg. partitionmagic) to partition your hard drive to install multiple operating systems in separate partitions as making these changes using FDISK is more involved. Partitionmagic also includes a bootmanager called bootmagic which makes multibooting even easier (nice graphical menu and mouse support).
This article written by Stephen Chapman, Felgall Pty Ltd.