QEMU is a open source emulator that has a port for all popular operating systems. You can download QEMU from http://lassauge.free.fr/qemu/release/Qemu-0.10.5-windows-Lite.zip.
All recent versions of Windows can unzip natively without an external program. If you have trouble unzipping the archive file, download 7-zip from http://downloads.sourceforge.net/sevenzip/7z465.exe.
Unzip the downloaded file to a folder. This can be a folder on a portable drive (like a thumb drive or an external hard disk drive). For the rest of this module, I assume QEMU is unzipped to e:\qemu-0.10.5-windows.
If you have administrative rights, you can also consider installing the kqemu accelerator. You can download the latest version (as of the time writing this document) at http://www.h6.dion.ne.jp/ kazuw/qemu-win/Kqemu-1.3.0pre11-install.exe. Once downloaded, run the installer executable to install the accelerator.
Because kqemu requires administrative rights to install, it is not as portable as qemu itself. qemu runs fine (though slower) without kqemu.
For the GUI-oriented, you can also download Qemu Manager from http://www.davereyn.co.uk/qem/setupqemuk60.exe. This installer includes both the emulator and a GUI-based interface to use it.