Let's start with giving you a doc link first. Everything you need should be here - http://blogs.vmware.com/vsphere/2011/10/vsphere-storage-appliance-vsa-useful-links.html
Now, the next thing you need to be aware of is that you must have vanilla installed ESXi 5.0 servers for the install to work:
- this means no running VMs, including vCenter. Your vCenter will need to be somewhere else while you do this install.
- this also means no additional network configuration outside of the default mgmt network. You cannot have a vMotion network already setup. So remove the vMotion network from the ESXi hosts
- you do not need shared storage; this is what the VSA will provide.
- the ESXi 5.0 hosts that are going to participate in the VSA cluster must be in a vCenter datacenter object. Have you added the ESXi 5.0 hosts to a DC?
- As you go thru the install screens, you need to select a datacenter from your vCenter inventory, and then you can select the hosts on which to install VSA. If the hosts are unsuitable, the VSA installer will tell you why.
Let me know how you get on once these items are addressed.
Cormac