In my experience there you cannot directly restore data from SQL 2005 into a SQL 2000 database (although you can do this the other way round).
However, you should be able to use the Copy Database Wizard to transfer objects and data. If you want to do this on a semi-regular basis then you can also use Integration Services/DTS. And remember that you can also replicate data to SQL 2000, so you could set up a snapshot publication on your SQL 2005 database. This can be scheduled too.