Default Parameter in Stored Procedure

Here is my Dilemma:

I am writing a stored procedure (in SQL 6.5) with a Default Parameter and will call this SP through Power Builder sometimes with a value for the default parameter and sometimes without a value.

I want the SP to update the appropriate column with the value when I call it with value and update the column with 'Null' when I call it without a value.

The SP goes like this

Create Proc dbo.sp_Emp
@ID int
,@AttorneyTrackID int = NULL
as
Declare @UserName char(8)
,@Now datetime
,@Status int
.....
....
.....



Will this work or is there a better way to do this. I hope I have posted enough info and expressed the problem clearly. I will appreciate any comment or feedback. I need help urgently, thanks.