I’m not familiar with MS OLAP, but somehow one little MS OLAP database silently run for seven years on department server that is under our administration control. The thing is that this database was actually (and still is) used by several end users all this time (almost without a hitch). Not something we can easily replace with something else or simply throw away.
I’ll post some essential links here that I found helpful during my preparation phase for the upgrade.

• Migrating Existing Analysis Services Databases
• Migration Considerations (SSAS)
• Known Upgrade Issues for SQL Server 2005 Analysis Services
• Upgrading or Migrating Analysis Services
• Using Upgrade Advisor to Prepare for Upgrades