When you convert a partition to NTFS, the resultant partition uses a 512 byte allocation unit.
If you have a second drive or partition, with sufficent space to temporarily contain your Windows NT C: partiton, AND you have enough space to install another copy of Windows NT (NOT on C:) THEN:
01. Create an updated ERD by running RDISK /S.
02. Install a copy to Windows NT to MaintNT or AltNT (or similar name).
03. Boot to this alternate install.
04. Copy the files on C: or back them up.
05. Format C: /FS:NTFS /A:2048 /V:Label (or /A:1024)
06. Set permissions on C: as (per tip 0395):
Administrators - Full Control
Creator/Owner - Full Control
Everyone - Change
System - Full Control
07. Copy the files back or restore.
08. Use Control Panel / System / Startup/Shutdown to set the default boot to your primary Windows NT.
09. Edit c:\boot.ini to change the text string of your alternate Windows NT to Alternate Windows NT (or similar) or delete the entries if you intend to remove the alternate install.
11. Using the ERD from step 01, Repair Boot Records.
12. Boot to your primary Windows NT and run FIXACL to set the default NTFS permissions.
13. If you removed the alternate Windows NT entry from boot.ini, delete the alternate Windows NT folder.
14. If you copied the C: drive folders/files to a temporary location, delete them.
15. Create a Boot Floppy.
NOTE: Some good reasons to keep the alternate Windows NT install are: