Windows 7 install on XP

[Bruce Stebbins]

I have a acer aspire one with windows I am trying to install windows 7 from an external hard drive. Every time I try to load it I get an error. Windows cannot retrieve information about this disk on this computer?

 

[Cycloid Torus]

I'm unclear about your situation.

You have made backup copies of all your data?
Windows XP operating system on an Aspire One?
Can read external HDD when booted in XP?
Bootable ISO for Windows 7 installation on an external HDD?
Aspire BIOS is set to boot from External USB device?
Boot from external HDD fails when?

Good description of process: http://www.pcworld.com/article/165159/Install_Windows_7_From_an_External_Hard_Drive.html