I am noticiing that I am losing HD space. One day it will be around 4.05 GB that I have then the next day I look it will be at 4.02 and now it is down to 3.95. I have not installed or downloaded anything the past week.
Go to Accessories - System Tools - Disc Clean-up. Highlight the drive you want to clean (usually C). When you hit OK another tab will appear with further options. Select System Restore clean-up and press ok. Your "lost" space should now be made available to you.
So why are you worried about 20 or even 100 Mb difference between days? More than likely this difference is simply explained by the Virtual Memory that is resized by the Windows system. Just look at the size of pagefile.sys.