Yesterday we went to install service pack 2 on a Windows Server 2008 machine. It turns out you need at least 5GB free on C: which we didnt have. After deleting everything we possibly could, including running CCleaner and making the Page File non-existant we were still 400MB off the mark.
Then I noticed a system file c:\hiberfil.sys which was 3GB.
Well it turns out that Windows Server 2008 still allocates space for a hibernate file. Who would want to hibernate their Live server?
Anyway, this is how to gain an exta 3GB...
C:\Users\Administrator>powercfg.exe /hibernate off