Bless you Paddy, it's not memory that is seing used, it's Hard Disk space.
Since you tried a system restore, I guess you are using Windows XP. So it's highly likely that, in the installation(s) you have been trying, a lot of files have been copied from the CD to your Hard Disk and the installation has then been done from there.
The location of these files is probably either:
C: \Windows\Temp (or similar), or
C: \Documents and Settings\fobotcso\Local Settings\Temp
Put your User name where mine is.
I'll bet it's the second. They're detritus and should be done away with after the installtion.