WinXP Restore Points

In WinXP, if the 12% (max can allocate) of my disk space equals 500MB and there are 20 restore points, where do I go to find out how much of the 500MB I have used already? I could have used 50MB, 100MB, 250MB, etc. I would like to keep track of thisso where do I get this information.

Also, if I have 20 restore points, and I use restore point number 12, does this mean that all of the changes that were made after restore point number 12 will be gone or only the changes made between restore points 12 and 13 not 12 and 20?