>i want to know the wallpaper file by using the registry key HKEY_CURRENT_USER\Control Panel\Desktop\Wallpaper.
>what function in the vfp's registry.prg can i call to do that and how ?

In VFP6 and later it's a Registry class.

#INCLUDE registry.h
oReg = NEWOBJECT("registry", "registry")
cValue = ""
oReg.GetRegKey("ResWidth",@cValue,;
		"Software\Microsoft\VisualFoxPro\6.0\Options",;
		HKEY_CURRENT_USER)
? cValue