Thanks a lot, I made the suggested changes and the SP is now working as expected.  I am very, very new to SP and now that I have my reports queries working on the VB side, I am moving them to SP to try to speed up the reporting process.

So you're VB code would look like this (take out the IF test and pass it even if the value is 0):

cmd.Parameters.AddWithValue("@pEmployeePK", tEmployeePK).SqlDbType = SqlDbType.BigInt
You can do something along the lines of the following to account for it in your SQL:
@pEmployeePK INT,
@pServiceCallsScheduleDate DATETIME
AS
BEGIN
SELECT DISTINCT 
dbo.ServiceCalls.*
FROM dbo.ServiceCalls AS SC
LEFT JOIN dbo.SC_Appliances AS SCA ON SC.PK_ServiceCalls = SCA.FK_ServiceCalls
WHERE   dbo.ServiceCalls.Status NOT IN (2,3) AND 
dbo.SC_Appliances.IncludeInSCRoute = 1 AND 
(@pEmployeePK = 0 OR dbo.SC_Appliances.FK_Employees = @pEmployeePK) AND 
dbo.SC_Appliances.ServicedDate = @pServiceCallsScheduleDate;
...
END
 
I accounted for the possibility of hte employeePK being 0 through the italicized where condition with the OR in it.  A
couple of things to keep in mind:
1) I used an OR above for clarities sake. ORs tend to slow things down in SQL, though, so if this is a query that
   is used a lot or that needs high performance, I would look at a different solution to handle this problem, even down to 
   having two seperate SQL queries on either side of an IF test.
2) I also have italicized your join and changed it to a LEFT JOIN, though that may not be what you need here. I'm not sure what exactly 
   your desired results are, but another thing to keep in mind is that OUTER JOINS are slow as all get out in SQL, and RIGHT JOINS aren't 
   typically used very much either (they are somewhat slow as well, though there are rare circumstances where they are neaded.) Depending 
   on what you are going for here, you can almost always get the records you need with a LEFT or an INNER join. 

I have the following store procedure in the DDT

@pEmployeePK INT,
@pServiceCallsScheduleDate DATETIME
AS
SELECT DISTINCT dbo.ServiceCalls.*
FROM dbo.ServiceCalls
RIGHT OUTER JOIN dbo.SC_Appliances
ON (dbo.ServiceCalls.PK_ServiceCalls = dbo.SC_Appliances.FK_ServiceCalls)
WHERE (dbo.ServiceCalls.Status NOT IN (2,3))
AND (dbo.SC_Appliances.IncludeInSCRoute = 1)
AND (dbo.SC_Appliances.FK_Employees = @pEmployeePK)
AND (dbo.SC_Appliances.ServicedDate = @pServiceCallsScheduleDate);
SELECT DISTINCT dbo.SC_Appliances.* 
FROM dbo.SC_Appliances
RIGHT OUTER JOIN dbo.ServiceCalls
ON (dbo.SC_Appliances.FK_ServiceCalls = dbo.ServiceCalls.PK_ServiceCalls)
WHERE (dbo.ServiceCalls.Status NOT IN (2,3))
AND (dbo.SC_Appliances.IncludeInSCRoute = 1)
AND (dbo.SC_Appliances.FK_Employees = @pEmployeePK)
AND (dbo.SC_Appliances.ServicedDate = @pServiceCallsScheduleDate); 

The parameter @pEmployeePK should be optional, which mean, that I can either pass a value or pass 0, in VB code I would simple do something like this:

If tEmployeePK > 0 Then
     cmd.Parameters.AddWithValue("@pEmployeePK", tEmployeePK).SqlDbType = SqlDbType.BigInt
End If

How would I code the same condition in T-SQL for the store procedure?