Setting SQL @ Variables From Within ASP

Hi, I have just started with ASP, and have a problem. I have created a stored procedure which looks to a specific tablename for information, based upon the users choice from a dropdown list.

The control works fine when executed from within visual web developer, and I manually enter the value that the variable expects. However I can not get the dropdown listbox value to be written to the SQL value. I have tried for days, traweled the net for answers, borrowed 3ft in height of SQL books! so either I am doing something fundamentally wrong, or I am missing something. My SP is:

ALTER Procedure GenericTableSelect

@tablename VarChar(20)

AS

Declare @SQL VarChar(1000)

SELECT @SQL = 'SELECT [base model] FROM '

SELECT @SQL = @SQL + @tablename

Exec ( @SQL)

and from the page the command to call it is:

 SelectCommand=generictableselect></asp:SqlDataSource>

But this fails to compile and comes back with "@tablename not defined"

any pointers in the right direction would help.

The object of this is for two drop down boxes - the first is populated from one database of categories, the selection of which populates the second drop down list with items from within that category.

 Cheers,


Richard