Should I make a yeast starter from dry yeast or should I just rehydrate it

I just pitch the whole envelope dry into cooled wort. I have re-hydrated according to Palmer's How to Brew also and did not experience a notable difference. Don't bother with a starter.

I'm making a high gravity beer so should I use two packets

What's high gravity?

1.059-1.069

that's not really considered a high gravity brew, one pkg of dry yeast should be fine, well one 11-15gram pkg should be fine. Some dry yeast come in 5-7gram pkg, if that is what you have then yes two pkgs would be required. Try looking at MRMalty.com he's got a goo calculator there.

yea high gravity is usually above 1.070. then i'd use to dry packets or a large starter with liquid yeast.

What would happen if you made a yeast starter like you would for liquid yeast but used dry instead just curious

dry yeast has all the components for yeast health drying into the yeast, the number of cells far surpass the number of yeast cells in a liquid vial. People do make starters with dry yeast, although there is debate over whether this is good for the yeast. You will get similar results as if making a liquid starter, but the true benefit of dry yeast, in my opinion, is the fact that you don't need to make a starter, the cell count is high enough that there is no need to step it up. I have pitched dry yeast directly into the wort for years and have always had good results.

Like many topics this is one where a certain amount of debate goes on. Some say it's good to do a starter even for dry yeasts, some say it won't make a difference, and still others would say it does harm. So you're unlikely to find out 'what would happen' but what different people think happens since there doesn't seem to be any firm consensus.

Remember that yeast has phases. You do a starter to get the yeast out of their dormant state into it's growth state and ideally pitch them at the point where they exit the growth state and start fermenting. As I understand it, putting dry yeast in anything but a huge several gallon starter would be too small for the yeast to really get to that growth state and really multiply. This is because of the higher cell count of dry yeast and the additional nutrients it's packaged with.

Thank you all

Also on the Mr. Malty site (www.mrmalty.com) is a section entitled "Fourteen essential questions about yeast starters". The third question from the top asks, "When shouldn't I make a starter?". Within that answer you will find this response about dry yeast:

"Another case where you generally don’t want to make a starter is with dry yeast. It is usually cheaper and easier to just buy more dry yeast than it would be to make a starter large enough for most dry yeast packs. Many experts suggest that placing dry yeasts in a starter would just deplete the reserves that the yeast manufacturer worked so hard to build into their product. For dry yeasts, just do a proper rehydration in tap water, do not make a starter."

The only dry yeast I have used is Fermentis US-05. Fantastic yeast, by the way. Here is a link to instructions for rehydrating the yeast prior to pitching.
http://www.fermentis.com/FO/pdf/HB/EN/Safale_US-05_HB.pdf

Hope that helps.