Conditional WHERE Clause

Hi,

[SQL 2005 Express]

I would like a DropDownList to be populated differently depending on the selected value in a FormView.

If the FormView's selected value (CompanyID) is 2, then the DropDownList should show all Advisers from the relevant Company.  Otherwise, the DropDownList should show all Advisers from the relevant Company where the TypeID field is 3.

Here is the SQL for case 1:

SELECT 
   AdviserID, 
   AdviserName
FROM 
   Advisers
WHERE 
   (CompanyID = @CompanyID).

Here's the SQL for case 2:

SELECT 
   AdviserID, 
   AdviserName 
FROM
   Advisers
WHERE 
   (CompanyID = @CompanyID) AND 
   (TypeID = 3).

Here's my best (failed) attempt to get what I want:

SELECT 
   AdviserID, 
   AdviserName 
FROM
   Advisers
WHERE 
   IF @CompanyID = 2 THEN
      BEGIN
         (CompanyID = @CompanyID)
      END
   ELSE
      BEGIN
         (CompanyID = @CompanyID) AND 
         (TypeID = 3)
      END

I've also tried:

SELECT 
   AdviserID, 
   AdviserName 
FROM
   Advisers
WHERE 
   CASE @CompanyID 
      WHEN 2 THEN (CompanyID = @CompanyID)
      ELSE (CompanyID = @CompanyID) AND 
         (TypeID = 3)
   END

and 

SELECT 
   AdviserID, 
   AdviserName 
FROM
   Advisers
WHERE 
   CASE WHEN (@CompanyID = 2) THEN (CompanyID = @CompanyID)
      ELSE (CompanyID = @CompanyID) AND (TypeID = 3)
   END

I'd be very grateul to know (a) what the correct syntax for this is and (b) if it can be achieved using a parametised query, rather than a stored procedure.

Thanks very much.

Regards

Gary