|As you've been told, memory & hard drive capacity are two completely different things. Your problem has absolutely nothing to do with memory.|
"hi its a dell inspiron 1520"
OK, we now know you're asking about a laptop rather than a desktop. From what I can dig up, it probably has a 120GB HDD with at least 2 partitions, C: for Windows (approx 100GB) & D: for Recovery (approx 10GB).
You really mucked things up by installing Vista to the D-drive. I won't even ask why you did that. You have no choice but to install it again, this time to the C-drive. You will lose everything so hopefully you have backup copies of any important data.
Follow these instructions: http://vistahomebasic.windowsreinst...