Adding A User/role To All User Database

Hi everyone,

I try to add a db_role or a user to all my databases with one script. Although parsing doesn't report any problem I get a Syntax error during execution.
I first select the database names into a #temp table which has two columns, ID and dbname.
After that I use the following code:

DECLARE @Count smallint
declare @dbVarchar(20)

SET @Count = 1

WHILE (@Count <=(SELECT MAX(ID) FROM #temp))

BEGIN

Exec ("USE @db")

EXEC sp_adduser 'test'
EXEC sp_addrolemember 'my_role', 'testrole'


SET @COUNT = @COUNT + 1
SET @db = (SELECT dbname FROM #temp WHERE ID = @Count)
END

It seems that the "Use @db" part has no value for the variable @db.
Does anybody knows how to solve this?