I guess you don't know what exactly these numbers stand for yet, do you?
Those numbers are the pixels that can be shown on it. So you would have 512x512 pixels, 256x256 pixels or 128x128 pixels.
When you have a picture wich consists of 512x512 pixels but you upload it on a texture item that can only show 128x128 pixels you would lose many pixels and thus the picture wouldn't be very detailed anymore.
As an example I made a picture of my had with two different texture items. The head picture itself consists of 300x300 pixels (what isn't very good, because I could have way more in it but whatever).
Last edited by gerFight; Aug 7, 2011 at 12:28 AM.
Reason: Uploaded the picture on ImageShack.us instead of pic-upload.de