Install Snow Leopard on Partition

Situation:
Mac Mini, mid-2011, 500 Gb (320 + 180) HD, OS 10.8.5 (Mountain Lion)
Snow Leopard DVD, purchased from Apple.

I am trying to install Snow Leopard (SLpd) on to a 180 Gb partition created with Disk Utility. The partitioning was successful and there is a second Mac HD image mounting to the Mini's desktop. Holding the Option key down at startup does not offer the option of the partition because it has no OS on it.

Connected to the Mini is an external Samsung DVD drive with double USB connector. The SLpd dvd is in that external drive, and successfully mounts to the Mini desktop.

I have tried booting from that external dvd drive with the SLpd disk in it by holding down the C key at startup, but it does not work. It continues to load to MLion. I cannot install SLpd to the partition, even though there is no OS on it. [I know about MLion and that it will not allow an earlier OS version to be clean-installed over it, nor can I buy MLion on dvd.]

Is there something I'm doing wrong, or not doing, and how can this installation of SLpd to the Mini's HD 180 Gb partition be achieved?

You should be able to just double click on the "Install OSX" icon on the SL DVD. It should restart the mini and then ask where to install it.

I'm sorry to let you know but you'll be like Don Quixote trying to get SL OS X 10.6.x installed and run with that mini model - it needs X 10.7 (11A2061) as a minimum.

See the similar or same specs here:
Mac mini "Core i5" 2.3 (Mid-2011) Specs (Mid-2011, MC815LL/A, Macmini5,1, A1347, 2442) @ EveryMac.com

Yes mate as pm-r says you cannot go back past Lion OS X.7 which is the operating system the Mini was released with. No going backwards alas.

Thank you for the replies. I knew about the 'minimum' Lion (10.7.x) or, in this case, M-Lion (10.8.x) issue, which is why I partitioned the HD, in the hope that I might bypass the block.

It's not a block. The ROM in that machine will not accept anything earlier than 10.7, period full stop.