I'm going to buy an iphone 3G and i have downloaded 55 apps and i want to know how many GB's all of them together are. How do i find that?

Open iTunes and select Applications from the left hand side. At the bottom of the iTunes window, it should tell you how much space all the applications together are consuming. Alternatively, once you plug the iPhone in and let it sync, then under the iPhone iTunes window, it will give you a break down of where all the space has gone. Space lost to music, videos, apps, other, etc.

it just says 55apps at the bottem of the page nothing else.

You can find out the total size of your iPod touch/iPhone apps using Finder. In a Finder window, go to your home directory and navigate to Music > iTunes > Mobile Applications.

Select/highlight the Mobile Applications folder and hit <command><i>

This works with iTunes 9.0.1 on OS 10.6.1.

i dont have an iphone right now, i am trying to figure out to either get a 8gb or a 16gb and i tried the "command i" all it said at the bottem was selected 55 apps of 55

You misunderstood. The instructions I provided above do not presume you have an iPod/iPhone. They simply tell you where to find the iPhone apps you've downloaded and how to measure their aggregate size.

need i say more?

thanks the picture helps alot more :) i found out that i have 2.32gb of apps