Hi, this is a 2nd suggestion how the text in
http://sagemath.org/download-windows.html

could look like:

Usage
To run Sage on Microsoft Windows you need the following:

   1. VirtualBox for Windows
   2. Download the "Sage" .ova file and follow these additional instructions.
 
The current VirtualBox solution provides you with an encapsulated and tested system. It allows to use the Sage notebook in your web browser with no noticable speed loss compared to a native Linux install.

System requirements:
512 MB RAM
2.5 GB free disk space


Other - unsupported - possibilities to run Sage on a Windows system:
Sage Live CD to boot from CD or USB
Community provided virtual machines: Gentoo, Puppy
Windows installer of the Live CD (install dual boot system)
Windows Installer of Virtualbox and Sage

Methods which were successfully applied in the past, but may or may not work for you:
Cygwin port of Sage
Ubuntu Wubi install
Andlinux/Colinux