I see there were no replies to this, so I'd just share some thoughts on this.
SME server is a full blown OS (well, sorta), in that it needs to format the HDD and install it's own set of scripts and packages.
Plesk on the other hand is a control panel, or just another piece of software, to be exact. You won't be able to instal SME server on a Plesk control panel. It won't work. You either need to use SME alone, and see if you can get Plesk to work on SME, which I wouldn't recommend since both SME & Plesk will want to do system admin, which is BAD, or use Plesk what it's meant for.