Probably not. The majority of computers sold in the last 4-5 years do not have the necessary driver support to run Windows XP. Further, if the system came with the 64-bit version of Windows 7, odds are it has more than 4GB of RAM, so your friend would lose access to anything over about 3.5GB using a 32-bit version of Windows.
He can go the other direction however, and upgrade to Windows 7 Professional or Ultimate and then use the XP Mode feature available. That is about as close as he will likely get.