Start by reading some material on Cluster (as well as replication) and also having a look through the Manual.
Once you have a better understanding of what Replication and Cluster can offer you, you may be able to come up with more precise questions.
From what you describe, it seems that Cluster could possibly be right for you, but maybe replication (or indeed, a combination of both) could be what you're looking for.
You may also want to have a look at consulting and training options. That can get you a lot of time with experienced people looking at your problem.
Stewart Smith, Software Engineer - MySQL Cluster
MySQL AB, www.mysql.com
Jumpstart your cluster:
http://www.mysql.com/consulting/packaged/cluster.html