Hard drive space is not "memory".  "memory" is the RAM in your computer.  If you are getting a drive "full" or no space left after you reinstalled Vista, perhaps you didn't reformat the hard drive before installing Vista and thus your old Vista installation and the new Vista installation are both on the hard drive?

We have no idea what is on your hard drive, or what has happened to the space on the drive.  Malware or spyware ould have even caused the drive to fill up. 

But, the best guess is that you didn't reformat the hard drive when you reinstalled.  Reformatting erases all the existing data and allows you to "start over",

Most likely you have a folder called windows.old on your hard drive.

In this folder of has all the old:

• Windows (from the Windows folders)

• Program Files (x86)

• Program Files

• Old user files

Move your old files from windows.old to the new location then delete the windows.old folder.