In microsoft SQL server you can create a linked server using the sp_addlinkedserver stored procedure. I am not sure what the correct arguments are for dbase4 but you can Google those or maybe look them up in BOL. Then you can just use your connection string to the SQL Server.
When you query the linked server you have to use OPENQUERY.
SELECT * FROM OPENQUERY(linkedservername,'SELECT * FROM ORDERS')
If one brings so much courage to this world the world has to kill them or break them, so of course it kills them. The world breaks every one and afterward many are strong at the broken places. But those that will not break it kills. It kills the very good and the very gentle and the very brave impartially. If you are none of these you can be sure it will kill you too but there will be no special hurry. Earnest Hemingway, A Farewell To Arms.