NTLDR is short for NT Loader, and is only associated with Windows OS from NT onwards/or dual boot situations.
Assuming you are not trying to dual boot (have 2 different OS's available on the same machine) then you have the incorrect bootcode on your hard drive, presumably left over from when the hard drive was used for running windows...
Dos requires a few more files - config.sys and autoexec.bat are not even required to boot - but they are hidden/system files.
Anyway, the easiest way round this is to get a bootable floppy with DOS on it (google for Dos boot disk, there are lots to download out there). I think a lot of people use DOS "7" or the version of DOS that windows 9x runs over. Then boot your machine from the floppy, and the command you need to run is "sys c:" assuming your harddrive is identified as c:
And yes, fdisk may be needed if there are problems idenitfying the drive. Fdisk can wipe and create partitiions for you, which you will then need to format ("format c:") before running the sys command....
Hope that helps....