it seems that for a "simple starter" (which i guess the wyeast packs are??)
No, a starter is a small quantity of wort, usually made with Dry Malt Extract (DME) at around 1.030-1.040 specific gravity. The Mr. Malty calculator can tell you the number of yeast cells you should be pitching and what amount of starter wort you need to achieve that. Wyeast packs are generally assumed to have a starting cell count of say 100B when 100% viable. You will almost never be working with a 100% viable yeast pack. The calculator allows for you to put in the age of the pack, which will help estimate what your viability actually is.
The amount of starter wort that you need to achieve the desired cell count is dependent on several factors including the number of yeast cells you're starting with, the volume of the starter wort, and how you handle it. A "simple" starter means you make the starter, pitch the yeast into it, and let it ferment out. Instead of say, putting it on a stir plate.
so, would i in fact need a second pack?
If you're making a starter then no. If you're not making a starter then yes.
Edit - If this is more confusing than helpful the bottom line is you can just pitch what you have. It'll make beer.