Holy Nova build is just an alternative to shadow and smite leveling. It is the aoe build. Its quite easy (with high level spirit gear) to grind through 4-5 mobs and still come out with almost full mana.
Your first 3 points should be spent in http://www.wowhead.com/spell=15336.
After that your build should look something like:
http://www.wowhead.com/talent#bVcbuhhiRG0cZZh:aV (Level 50)
At level 50 you split away from the discipline tree and start putting points into holy to further buff Holy Nova:
http://www.wowhead.com/talent#bVcbuhhiRG0cZfxx0bbZh:aV (level 69)
At level 69 you can start filling in some other dps spells (try to buff your Shadow Word: Pain because you will use it a lot anyways for mana regeneration thanks to the glyph and the buff to damage on multiple mobs). You can also buff your hit chance and pick up mind flay to help with runners:
http://www.wowhead.com/talent#bVcbuh...x0bbZhxf0o:aVh (level 80)
As for gear, you are going to want to focus on mana regeneration for easy and quick leveling. Spell power is nice but not as nice as having mana to cast spells. Your items should reflect this. Stacking spirit and intellect as much as possible is a must. Items with intellect, spirit and spell power are awesome for this build.
So far I'm level 40 with this build and its going really well. I'm able to heal instances as the main healer and still decent dps. Its not uncommon to be above one or two of the dps when I'm healing. When I'm actually dpsing I'm coming out on top and you can easily do both with this build. The single target dps isn't horrible (especially if you are stacking haste), but this is an aoe build hence why I made decisions like not taking Power Infusion since all of the casts will be instant for the most part.