Stored Procedures - Restricting Access

Hello everyone,

I have a design problem which I am hoping somebody can shed some light on.

I am running SQL Server 2000 using SQL authenticaiton (due to be changed to Windows authentication in the next 6 months). I have a table in my database which we shall call monthly. I want to restrict the ability to insert to the monthly table to 2 stored procedures (proc_abc & proc_xy) which I have written which do various other validation checks before it inserts the data into monthly.

Users with the Foo function assigned are able to execute proc_abc & proc_xy

I have written a VB application which can be used by users who are not familiar with SQL to be able to execute these stored procedures. (Must have Foo function in order to login to this application).

I want to restrict the ability to execute the stored procedures to users using the VB application only, and thus not be able to execute the stored procedure using Query Analyzer or such like for any Foo user.

Is there anyway I can do this?

One suggestion put to me is two split the functions. Have one function lets call it Top which can access the VB application and then have another function called Bottom which is able to execute the stored procedures. Only the VB app would have access to the Bottom credentials. But is this secure? Would I just hard code the credentials for the Bottom function user within the VB app? This doesn's seem a secure way of doing things to me.

Thanks for the help!