Make sure your c: is fat16 (not fat32). install NT. Personally I prefer to keep it on a seperate hard drive or partition, that way you can use NTFS for NT and still run DOS/win95. If you are going to work with NT professionally, you should be familiar with the security features of NTFS.
Once NT is installed, go to control panel-system. select teh startup/shutdown tab and you can select the default OS and amount of time before it is automatically selected.