Here's a utility I use to check for duplicates. It doesn't absolutely have to have a tag on the field you're checking on, but it would be optimized if there is one.

* Chk4Dup.prg		(c) 1999, Peisch Custom Software, Inc.

lparameters pNewVal, pFld

local lFnd, lOldRec, lOldAli

lFnd = .F.
lOldRec = recno()

lOldAli = alias()
select 0
use dbf(lOldAli) again alias DupChk

locate for eval(pFld) = pNewVal
if found()
   do while .T.
      if recno() = lOldRec
         continue
      else
         lFnd = .T.
         exit
      endif

      if eof()
         exit
      endif
   enddo
endif

if lFnd
	messagebox('Cannot enter duplicates in this field',48,'Duplicate found')
endif

use in DupChk
select (lOldAli)

return not lFnd
*-------------------------------------------------------

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>I am trying to create a form containing personnel data, which allows the user to search via first or last name. At the same time, I am trying to allow the user to enter a new entry, but let the system prompt the user if that new entry has already listed in the table (double posting). I have the search taken care of (I am using a self created class for that).
>
>I can't seem to quite grasp the double entry method w/out killing that class. In my mind, I know I need to use a SEEK command, but that as far as I can get. Any ideas would be VERY helpful!!