Today I tried to install Vista SP 2 and the installer informed me that I did not have enough free disk space. Hence, if you don’t want that the same thing happens to you, you must make sure there is enough free space on your computer’s hard disk prior to install the service pack. The minimum disk space requirements for SP2 depend on what method you use to install SP2:
Via Windows Update:

x86-based: 650 MB
x64-based: 900 MB

Downloading SP2 from Microsoft’s website:

x86-based: 1900 to 3000 MB
x64-based: 3300 to 5000 MB

1. More free Hard Disk space after installing Vista SP 2
2. Windows 7 Official Requirements
3. VISTA SP 2 on Windows Update
4. Windows Vista to Windows 7 upgrades
5. Windows Vista Tip