you can't just install it on a default Redhat machine install. It needs to be partitioned a certain way with certain services enabled/disabled. Good luck getting Rackshack to re-install your machine with that specific partitioning cause they wont! They sell you as-is machines. They do sell servers with Ensim pre-installed for you though at no monthly fee. I reccomend that. Got 2 with them that way and have had no problems. Just watch the buggers when they try to get you for bandwith overages they can't prove you used!
The only place i have found that will partition a server to your needs is FDC servers, although i haven't been able to install Ensim on my box there, others have.