I am the main contributor of standalone Windows builds of the Electrum Bitcoin client.
These builds support all modern Windows OSes (2000,XP,Vista,7).
I maintain a portable version of the latest stable build at:http://dre.tx0.org/elecwin.htm
(this is the windows build homepage, with version number, release date, SHA-1 checksum, links to screenshots, downloads, and source code)http://win-electrum.googlecode.com/file ... rtable.exe
(direct download link to the current portable release, version 0.53-2)
I hope you like it, and do not hesitate to let me know if you find any issues with the portable version!
For more information about the Electrum open-source client, and more download links, see the official website