i have a la spa hot tub the dimensions are approx 8x8. what type of support do i need?

That largly depends on how your spa base is made up. If you figure, a 7'x7' spa will run roughly 300 pounds dry, and add in 400 gallons of water, at about 8 pounds per gallon, which is another 3200 pounds, and add in occupants, max at 8, average of 160 each, for a total combined weight of 4,780 pounds. If your spa has a full sized base, completely supporting the entire contents, you would divide it's square footage into total weight, bringing your weight to 97 pounds per square foot. The average person exerts a pressure of over 200 pounds per square foot. Now, if your deck is built properly, this will be no problem, as most decks are built to withstand a minimum force of 500 pounds per square foot (in my area). Now, if your spa sits own it's base, basically the footwell, you are looking at about 300 pounds per square foot, and pesonally, I wouldn't try it without reinforcing that section of the deck with additional supports. I like double the room for error, so to speak.

Follow up question - which type of spas "sits on it's own base, basically the footwell"? The spas I am considering are the Jacuzzi 365, Hotsprings Vangaurd, Hotsprings Grande, possibly a Sundance. I believe these have bases that distribute the weight over the whole foot print.

The deck I am planning should be very beefy. 4x8 beams spaced 3.5" apart (basically puts a beam at each end of the tub and one in the middle), 2x6 joists on 12" centers and 9 footings (3 for each beam) which are 8" in diameter and 4' deep.

Thanks!