I fully agree with brother Javafan++, clustering is probably not going to do you any good. My personal experience with clustering is not too positive (read: a lot of effort ending up with "virtual fail-over").

I am not sure if replication is the solution though. It seems you don’t want to stress your DB and the idea is to make a copy of it to do your work against? There are several ways of doing that. It can be as simple as dumping the database and rebuilding it elsewhere. How big is the database? How up-to-date does the data need to be? Maybe you have to think in the direction of a data warehouse solution?

If you use SQL Server there are (decent) replication solutions available. You can check MSDN for a starter. I have to add that replication solutions always take * effort * to implement and that it often has a negative impact on overall performance as well.