Is there a way to downgrade from Vista to XP Upgrade Version when you don't have a previous OS CD because when i try to do it XP setup will not reconize the Vista CD as a previous OS?

You do have the upgrade version of windows XP...right? You can force the test to read itself as the previous installation. This was a default that was purposely allowed just for that case. Save everything you wish to save to another drive or to CD/DVD. As you must perform a clean installation to perform the deed. Reboot with the upgrade installation CD and follow the prompts for a clean install and when prompted for showing the required OS you can browse to the CD/DVD rom that the disc is in and it will see the upgrade installation disc and accept it as a previously installed operating system and will then continue the installation. It is the disadvantaged who habitually elect Democrats on the belief of personal change--- yet they remain disadvantaged.

Are you trying to install XP on a Vista machine? If so you'll need an XP CD, NOT an XP Upgrade CD. An XP Upgrade CD is meant to be used to upgrade a previous version of Windows. Vista isn't a previous OS. It's newer than XP. Keep in mind too, that if you do have a Full XP Install CD, you'll need to backup your data and also make sure that eMachines has XP drivers for all the hardware installed in your machine. Otherwise, you'll be in trouble when it comes to installing video/audio/networking, etc. "So won’t you give this man his wings What a shame To have to beg you to see We’re not all the same What a shame" - Shinedown