ASUS released a clever tool called AutoC2D that helps you transfer whatever you installed onto your Eee PC - with Windows installed - from your C drive to your D drive. This means you get a lot more space for Windows Update, programs, or games that you wish to install.
AutoC2D automatically sets up partition D (D:) as the default path for the Program Files folder. The C:\Program Files folder becomes a soft link, which synchronizes with D:\Program Files.
Software will be installed only in D:\Program Files even if you select C:\Program Files as the installation path.
This tool requires Windows Server 2003 Resource Kit Tools, which you can download here.
You can download AutoC2D here (please read the included manual 1st).