BDE Searches Slow in international character sets

Please, a need help.
I'm working with Delphi 3 and the BDE and Interbase 4.2.
I create a Database with Default Charset WIN1252 or ISO... for Spanish
sorting.
I create a table CUSTOMERS with a few columns and a primary key...
I create indexes for the columns defined as COLLATE ES_ES or COLLATE
PDW_SPAN
When I Execute:
Customers.Locate('NAME','CAL',[iopartialkey]) with 40.000 records, it seems
that searchs sequentialy because it takes a lot of time (20 seconds).

Where Customers is a TTable nor a TQuery

But if I execute Through IWSQL:
SELECT NAME FROM CUSTOMERS WHERE  (NAME LIKE "CAL%")
IT'S VERY QUICK!!!
I tried to change the alias Language driver to Spanish ANSI and others....
If I select NULL alias language driver the characters dont display correctly
and I have errors.

When I use a database created with CHARACTER SET NONE and using the locate
procedure, the result becomes immediate.

I would be very gratefull if somebody could help me,
   Yours faithfully,
            Toni