You cant go wrong with mtpockets, sucmnsee, or bobs image backups that are in the zgemma 2s forum on here. Just download and flash. Everything is already set up for you. I prefer openatv as you can update it. sucmnsees VIX image is perfectly good though.
If you want to do it from scratch (which is a great way to learn)
http
://images2.mynonpublic.com/openatv/current/index.php?open=zgemmas2s
Download latest version unzip and copy the zgemma folder to a freshly formatted usb stick.
Place in zgemma, turn on and press the front standby button when it says usb on lcd.
The next bit I am doing from memory so excuse any mistakes.
This is a brief summary as all detailed information can be found in various threads on this forum.
After install go to plugins menus (green button) and download these plugins from extensions folder.
Cacheflush - to keep your boxes cache clean
xmltvimport - epg data
Download this skin from the plugins skin folder
openvix-blue-hd - this is the sky skin
Download this from the plugins systemplugins
autobouquetsmaker - this is your tv lists, i.e sports / movies sections etc.
I can't remember if you can download softcams from these plugin folders.
if not google "softcam-feed-mipsel_1.0_all.ipk"
FTP this to your tmp folder and then load it. Menu... setup... Software management... Install local extension (or blue button... plugins... ipk installer)
There a plenty of guides in the downloads sections for zgemma on the backup images mention at the beginning that will step by step you through the rest of the set up including how to set up softcams with your line and how to correctly setup your autobouquetsmaker.