Howto load balancing

What kind of traffic levels are you planning for?

There are various load balancing techniques around ranging from the free to the very expensive, and the inefficient to the highly effective.

At the lowest end of the scale is simple round-robin DNS. You configure your site's address with two IP addresses and the DNS server alternates between the answers. This gives you a crude load balancing option - there's no direct control over which server gets the traffic, levels may be uneven and, worst of all, there's no redundancy in case one server is down - the DNS server will continue to hand out it's IP address. Its advantage, though, is that it's free.

Moving up the scale a little there are various Linux based solutions that can do simple load balancing through its IPTables (or ipchains in older distributions).
I've never used them, so I don't know how effective they are.

At the top end of the scale are load balancing appliances such as those from F5, Cisco, NetScaler and others.

These move up the price chain a fair way but offer far more features, server health monitoring (to make sure the server is able to service the request), advanced load balancing rules to decide which server should handle the request, and multi-gigabit per second throughput.

If you just have a couple of servers, the appliance path may be overkill, although if you expect to grow then it may be something worth considering.

As for the replication question, there are many ways of doing that. At its simplest level, rsync can replicate a directory or filesystem using an efficient protocol that just transfers the differences. It's included in Mac OS X and the man page gives examples of its use.