Lenovo is making downgrade from Windows Vista to Windows XP easy by providing Windows XP Recovery CD media. This is valid until July 31, 2008.
In an excerpt of their online guide:
Have a Microsoft Windows Vista Business or Microsoft Windows Ultimate system, but need to continue using Microsoft Windows XP for a while? For a limited time Lenovo is providing Windows XP Recovery CD media as a way to downgrade from Windows Vista. Lenovo customers that have Windows Vista Business or Windows Vista Ultimate “qualified systems” may purchase a Windows XP Recovery CD until July 31, 2008. Fees may vary. Please contact your local Support Center for additional details.
“Qualified systems” are Lenovo notebook and desktop systems purchased with a Windows Vista Business or Windows Vista Ultimate preloaded operating system.
There will be a limit of one Windows XP Recovery CD set per customer, per serial number for each system series with preloaded software, including Windows Vista Business or Windows Vista Ultimate.
The downgrade page is here.