well i'm sure many people here could handle this question, but i'll give it a shot anyway as it was addressed to me (-:
open my computer, and (assuming you have one major hard drive, C:), right-click the C: icon, and click properties. it'll tell you the total drive size, and the free space available. what are these values? are there any other hard drive icons there too (you may have several physical drives inside your machine, or you may only have one that can be split into several pretend drives [partitioning])?
if you have plenty of free space on your C: (assuming that's the main drive), i.e. more than 2 or 3GB spare or so, then it may just be the file itself. try downloading it all over again, and installing it again.