How to run Windows XP under Ubuntu Linux

QEmu can run an OS inside another OS - for example, Windows under Linux. QEmu uses kqemu, an acceleration driver included in Ubuntu 7.04 Feisty Fawn to run Windows at usable speed.

Ubuntu 7.04 Feisty Fawn also includes a new version of rdesktop that can be used to start individual desktop apps from the VM on your normal desktop. See SeamlessVirtualization.