What OS X software is installed on the box? OS X, or OS X Server?
If it's a newer OS X version and you want OS X Server from the installer disks, wipe the disk and reinstall.
Officially, it's not likely that a recent Mac Mini Server would even officially support something as old as OS X Server 10.6; here's the list of the minimum versions (HT1159) — I don't see a June 2012 model, the closest to that acquisition date would probably be a mid-2011 Mac Mini or Mac Mini Server model, and those require OS X or OS X Server 10.7, or later.
OS X 10.7 also didn't usually arrive with DVD disks, so that may be an old DVD from some other box.
To confirm the Mac Mini model, see > About This Mac > More Info...