[MAXIUM]

Muchisimas gracias por vuestro código, dime como puedo modificarlo para además solo permita valores negativos es decir solo un singno '-'

Yo usaba este código:

Código Delphi [-]
If key in ['-',','] then
     case key of
          '-': if (length((sender as TEdit).Text)>0) then
               if ((pos('-',(sender as TEdit).Text)<>0) or
                  ((sender as TEdit).SelStart >0))
               and
                  ((sender as TEdit).SelLength <> length((sender as TEdit).Text))
               then key:=#0;
          ',': if ((pos(',',(sender as TEdit).Text)<>0) and
                  (pos(',',(sender as TEdit).SelText)<>0))
               xor
                  (pos(',',(sender as TEdit).Text)<>0) or
                  ((length((sender as TEdit).Text)>0) and
                  ((sender as TEdit).Text[length((sender as TEdit).Text)] = '-')) or
                  ((sender as TEdit).SelLength = length((sender as TEdit).Text)) or
                  ((sender as TEdit).SelStart = 0)
               then key:=#0;
     end
     else if not (key in ['0'..'9',#8]) then key:=#0;