You only need to do this if you're getting serious amounts of traffic. A well configured server can easily handle over 100,000 visitors per day.
But in case you wanted to know, here is what you would do. In reality you would want to purchase all three servers from the same datacenter, to reduce latency and bandwidth usage.
Setup one server to handle mysql and make sure it can accept connections from ip addresses other than localhost.
Setup the other two servers to handle http connections. The issue is that really, you need a further server in order to load balance between the two http servers. That being said, you could just as well set one of them as the load balancer and then have it distribute traffic between its own web server running on localhost and the other web server you have.
If this is sounding a bit complicated to you, don't do it!