It is not entirely clear:
— why do you need a DBMS (development, delivery along with deployment on the server of the enterprise);
— on what hardware you're supposed to put your DBMS (number of processor cores, amount of RAM);
— size of the database (in bytes and in the number of records);
— the ratio of actions when accessing the database (read, insert, delete, update);
— for more specific information.
I think between MSSQL 2005 standard and Workgroup. What to choose, how much and where can you buy?
Well, of course standard version is better (or rather less restricted). For the rest in the know — did not have to face.
So in conclusion: I am sure that you have considered Express version — it is not fit?
Perhaps the answer to this question will be the answer to your question.