Then configure two services in the cluster, both forwarding. The cluster will then assign one service per box. If the dns supports round robin it will hand out both addresses to half the users each. I am setting them up as a forward proxy cache. I have read about setting up the cluster, but can't find if the cluster is fail-over or load balanced.
Cluster is fail-over only, no load balancing.
As a workaround you can point the browsers to the proxy via dns name. Go into your dns server and configure it to hand out two ip addresses for the proxy. Then configure two services in the cluster, both forwarding. The cluster will then assign one service per box. If the dns supports round robin it will hand out both addresses to half the users each.