How to use decode on the value part ?

Question

i have a query
select
     col1, col2, col3
from
     tab1, tab2
where
     cond1= 'parameter1'     
I need to modify this query to use a decode function instead of this parameter1.
something like
select
     col1, col2, col3
from
     tab1, tab2
where
     cond1= decode(parameter1, 'x','val1','val2')
How can i use such a decode function on the value part ?
IF i try this, it gives me no data found error....
The following is also not working..IS there a way to do such cases ?
select
     col1, col2, col3
from
     tab1, tab2
where
     cond1= ( select decode(parameter1, 'x','val1','val2') from dual )

Answer 1

Of course it works...
test@ORA10G>
test@ORA10G> drop table table1;
Table dropped.
test@ORA10G> create table table1 (
  2    name        varchar2(50),
  3    condition1  varchar2(2),
  4    condition2  varchar2(10)
  5  );
Table created.
test@ORA10G> insert into table1 (name,condition1,condition2)
  2  values ('Hi there!!','xx','VAL1');
1 row created.
test@ORA10G> commit;
Commit complete.
test@ORA10G>
test@ORA10G> select * from table1;
NAME                           CO CONDITION2
Hi there!!                     xx VAL1
1 row selected.
test@ORA10G>
test@ORA10G> declare
  2    CodeL varchar2(3) := 'AB';
  3    CodeName varchar2(50) := '';
  4  begin
  5    select decode(CodeL,'AB','VAL1', CodeL)
  6    into CodeName
  7    from dual;
  8    dbms_output.put_line('CodeName: '||CodeName);
  9    select Name
10    into CodeName
11    from table1
12    where condition1='xx'
13    and condition2 in ( select decode(CodeL,'AB','VAL1', CodeL) from dual );
14    dbms_output.put_line('CodeName: '||CodeName);
15  end;
16  /
CodeName: VAL1
CodeName: Hi there!!
PL/SQL procedure successfully completed.
test@ORA10G>pratz