Note that Windows 8 has just been launched and this is totally different from Windows 7, and any earlier release of Windows.
I went into John Lewis, Comet and Currys yesterday and those shops are already full of Windows 8 PCs, and they are selling off their Windows 7 PCs in a "Windows 7 clearout".
So if he goes to one of those shops quick he may get a bargain.
Dell are fine, but even they may have shifted to Windows 8 so he may have trouble getting a Windows 7 PC from them.