modern HD's map out bad sectors internally, without ever notifying the OS;
to view that info you'd need a diag tool from the HD maker. If the
drive supports SMART that info is in there, and a SMART tool (some
versions of norton) can display that info.
Once the HD's built-in reserve of spare sectors is used up it starts
reporting the read/write errors to XP, which then maps out the bad sectors
on its own; these are the bad sectors reported by chkdsk. If the HD gets
to this point it's pretty much doomed, and should be monitored closely and
replaced if the chkdsk bad sectors count continues to creep up.