Extend the OS disk the easy way (ExtPart.exe). The ExtPart utility provides support for online volume expansion of NTFS formatted basic disks. Before installing ExtPart and extending a volume, ensure that you have a working backup of your operating system. It's only 40Kb and free :-)
extpart [volume size]
volume - the volume to extend. e.g. f:, g:, etc (only basic volumes)
size - the size in megabytes by which to extend the volume.
Example:
To extend the g: volume by 1 GB (1024 MB) use the following command:
extpart g: 1024
Screenshotās and a Dutch 'how to' are available at Arne Fokkemaās ICT-Freak.