Hi @ns_nirosh
I have an howto ready made some months ago for my personal use but it is written in italian 
Basically you have to:
1) create your storage pool of DIR type when there will be created HDD images of VMs
2) create your storage pool of DIR type for ISO of your operating system CD/DVD
3) enable WebVirtMgr console from Nethserver admin Web interface
4) to install Windows 7/8/2008/2012 you must download guest drivers ISO from http://www.linux-kvm.org
5) configure bridge interface within NethServer admin Web interface not from WebVirtMgr
My suggestion is read steps from 1 to 6 and sort them in the right order, I mean: prepare/download ISO, configure the environment etc.
Hope this can be useful to start.