The Bart PE Builder software utility takes Windows XP and shrinks the OS to your USB flash drive. Besides converting your mini- drive into an emergency boot disk, you can use the utility to load a Web browser, media burning software and more – to have handy anywhere you go.

And by the way, no it doesn’t violate the Windows XP EULA, so if you have a USB Pen Drive and a Windows XP CD why not give The Bart PE Builder a try and see how useful it really can be in a wide range of circumstances.

PE Builder Project home page
Article at Tom’s Hardware Guide