not sure if this belongs here

I have a web cam and have been happily streaming my face using msn messenger. but it just ooccurred to me that i am uploading a heap of data and according to my isp if i go over 3 gig a month it costs me$$$...so the question is for about 10 mins worth of stream how much have i used or created??? is there a way to make frame size smaller or a better codec to minimise this ....how to i set the codec for it using msn...msn must use a codec to compress on the fly then transmit......help