On another note for using the CD booting in 486 : You can use Smart Boot Manager or Plop Boot Manager to redirect booting sequence to a CD drive. I'm using Smart Boot Manager in my 486.
Booting to Ultimate Boot CD opens up the ability to use tons of utilities, especially when it comes to HDD Diagnosing, Partitioning and Advanced HDD editing.
If going through Boot Managers seems like a hassle, you can boot it in yout modern machine, load up the particular utility or tool you're interested, and exit to dos from within the loaded software screen. It will drop to the command prompt with the loaded directory. You can then copy these files to a floppy disk and use them in your 486,386,286,XT,etc.
And of course, all the tools available in the UBCD are available separately on the net.
And I don't think Norton Disk Doctor is enough for the jobs you mentioned.
Seagate, WD, and Maxtor - the probability of seeing your hard drive falling into one of these groups is very high, and as others mentioned, all these three have dos level testing and repair utilities from their respective companies (which are all, again, available in the UBCD - including those for Samsung drives.)