You can't "direct the stored procedures to run on the client", so forget that idea. Stored Procedures run on the server engine.

Leaving aside the question of whether it would be cheaper to upgrade the server than to reproduce in vb.net what these stored procedures do ...

There are quite a few ways you could duplicate what a stored procedure does and make it all run on the client side.

One option to consider is pulling all the data you want to work with out and temporarily writing it to local database files, say an Access .mdb - and then doing the joins/updates/combines on that file. That would probably be a whole lot easier than trying to create an entire virtual database structure using in-memory datasets/datatables.