Load Balancing?

[Kirk]

We are currently reviewing different load balancing options for our growing MySQL installation. A few questions have come up that, and since I am not a mysql specialist by any means, I am struggling with possible answers. Hopefully someone here can shed some light on these issues and help me find a solution.

The original code/database was never written to be distributed. Consequently we have had trouble setting up any kind of distributed services. We have a single master that replicates to several slaves. These slaves are not used except as a backup/hot spare. Since we have not been able to split up the updates and the queries, and we can't update to a slave, we are stuck using just the master. We are rewriting the code/database structure to allow that kind of modularity, but it is a long process.

The alternatives I am considering are:
-Some kind of multi-master replication. I understand 4.x has some of this capability but I don't know what is required to make it function. If the code would have to be written around it or not.
-A native MySQL cluster. This is pretty new and I doubt we will adopt it because of the memory/size limitation. But if someone has some input I would really appreciate it, as my knowledge here is especially limited.
-A third party layer to provide MySQL clustering ie. Emic Networks, or similar. I have no experience with these either, and I don't know what kind of caveats there might be with such a product.

Any input is appreciated,
Kirk