Espero esto sea lo que buscas
Código Delphi
[-]function insertCharacter(number:integer):string;
var
str:string;
begin
str:=inttostr(number);
if length(str)>2 then Insert(',',str,length(str)-1);
Result:=str;
end;
var
numero:integer;
begin
writeln(insertCharacter(123456));
writeln(insertCharacter(123));
writeln(insertCharacter(1));
writeln(insertCharacter(123456789));
readln;
end.
Saludos..
edito:changos eficsia me gano XD