Running 2005 AS on 2000 DB, or should I upgrade 2000 Server to 2005?

I have searched a bit and read some threads, but want to clarify

I want to create Data Mart/Warehouse to use with SQL 2005 Analysis service

Questions:
Is there any problem using SQL 2000 Database as backend?We do plan to upgrade to SQL 2005, will there be problem in migrating the analysis service?Can I run 2005 AS stuff on SQL 2000 database? like creating cube, data mining model?I want to run Predictive Model/Data Mining Model on it as well, do they work on 2000 DB?I guess in short
Should I upgrade the server to 2005 before I start playing with 2005 AS?Can I start with 2005 AS on 2000 DB, then upgrade 2000 DB to 2005 whenever?
Thanks, any help is appreciated greatly

Is there any problem using SQL 2000 Database as backend?