For changing over the new euro European currency unit there is a new IMG as of Release 4.0B. In it you carry out all procedures in connection with European Monetary Union.
In contrast to the IMG norm, activities which do not affect the Customizing of your system are also contained in the Euro IMG. This has the advantage that you can carry out all activities which are necessary for the euro changeover at one place in the system.
You can find the Euro IMG under Cross-Application Components -> European Monetary Union: Euro.
You can find more information on European Monetary Union and the changeover to the euro currency unit associated with it in the R/3 library under CA Cross-Application Components -> European Monetary Union: Euro.