By downloads I meant simply looking at my disk space right after starting up windows xp. I could click on my computer and keep clicking on refresh until the avast pop-up comes up telling me my system has been updated (I have it set to automatic) and I could see the disk space going down until that point, often at least by a hundred megabytes. As another point of reference, when I would take my laptop on vacation where I had no internet access and no updates could be made, my disk space stayed exactly where I had left it the week previous, save a small increase caused by downloading photos from my digital camera.
I'm curious about the mention of "unpacked updates" and cleanup that is supposed to happen, as I have seen some unexplained recovery of space every now and then, but it certainly doesn't happen on a daily basis. I couldn't even guess if it's even a regular occurrence.