Do I need to have an intake if I am only using part of the room?

I am setting up a flowering area aproximately 10'x5' that I plan on running two 600 Watt HPS.

I am exhausting outside using a 462CFM inline fan that's pulling through a carbon filter.

The flowering area will not be air tight (using black tarp nailed/vecro'd to a makeshift wall frame).

What I am wondering is if the fan will pull air from the room through the areas where the tarp used to block the light is not air tight?

I could make an intake pulling from the attic, but the room that I am growing has an AC/Heat vent, so it would be easier for me to keep it cool up there during the summer if the fresh air was coming from the room.

No you should be fine it is more important that the stagnent air is exaust out of the room.A couple of fans inside the room will do for fresh air.

make sure your intake (whatever comes from the tarps) can flow faster than what you vent exhaust or you will put some stress on your vent and it won't reach its potential.

Would it be recommended to put a few inch piece of dryer vent on the floor through the tarps to create a dedicated path for incoming air? The 462CFM inline fan is pretty heavy overkill, from what I've read other people recommending it would have been sufficient for a much larger room and much larger carbon filter than what I am using (My carbon filter is rated for around 270CFM).

I'd just much rather pull my intake air from the room (which is heated in the winter and has central air in the summer) rather then pulling attic air that is going to be the opposite and make it harder for me to control temps.

your carbon filter will not filter half of the smell, and it will need a carbon refill really quick.
don't use it with that vent, use a matching carbon filter.

You can use whatever you want that can let enough air move. You would probably want it to be light-proof though.

I was mistaken about the carbon filter and fan. This is the pair I have here:

http://htgsupply.com/viewproduct.asp?productID=52609

I have a small peice of 6 duct connected my flowing and veg rooms, and a 6" duct going from the veg to flower rooms. Everything is light-proof, however the 6mil plastic sheeting that I am using for two walls s just stapled in place with a staple gun, so air can pass through the seams of the plastic sheeting however any spots where light was leaking I sealed with duct tape.