Vassili,
What exactly do you mean by "migrating the enitre database as a cube"? Generally speaking, when you migrate a cube from 2K to 2005, the calculated measures will be migrated as well. However, if you are not migrating the database, and build the database from scratch and change the design, then you will have to manually re-create the calculated measures.
Can you provide more details, please?
Yaniv