In our environment we are running BES 5.0 on Win 2k3 SP2. I would like to set up high availability so if that server goes down the new server will start all services automatically. Can I setup the new server to be Server 2008 R2 or does it need to match the same OS version of the old server?
Currently the server is running SQL server express. I would like to find out what steps should be taken when setting up the H.A. Do I first need to run the setup of the BES server software on the new VM or do I need to install and configure the new version of SQL server on the new box? By the way the old server is also a VM. Do I also need to remove the version of SQL server express on the existing BES server? Any details you can give in regards to configuring or any articles you can point me to would be greatly appreciated, thank you.

i don't think server OS matters but if you run SQL server express you will need to somehow mirror that and you will need SQL server standard at least. i think you will need to sort that out first, once that is done you can look at installing the bes HA server. the bes 5 guide is an excellent resource for this, during the installation on the HA server you can specify it is an HA server and just follow the steps. but i think you need to sort out SQL first