Hmm... well, I wouldn't say that it's 'eating' it up. It's like this:
You get 10Mbps from your ISP. Your router has the function to give that to you in either wired or wireless format. Wired is faster and more reliable, though less convenient. Wireless is slower and shared, so each device will take a portion of that pool of speed. If you have two devices on a 10mbps wireless connection, each would get roughly 5mbps. I'm not sure if there is a loss from the ISP/router to the wireless adapter though, so your wireless speeds might actually be lower.
Now, if you are, instead, after the actual amount of data being used by your wireless card (as opposed to the speed), then you will likely need to monitor it with software. I know windows xp has a dialog box for some of the network icons that depict how much data has been sent and received.
Hope that helps.
-9to5