use warnings;
use Win32::API;

my $SystemParametersInfo = new Win32::API("user32","SystemParametersInfo",[ I,I,P,I ],I);

if (not defined $SystemParametersInfo ) {
	die "could not import SystemParametersInfo";
}
my $wallpaper = "c:\\winnt\\Blue Lace 16.bmp";
my $action = 20; #reference http://support.microsoft.com/support/kb/articles/Q97/1/42.ASP to see which constant to use
my $saveWinINI = 0; #save this in the user profile?
my $param = 0; #dependent on what $action is

#change the wallpaper
my $retval = $SystemParametersInfo->Call($action,$param,$wallpaper,$saveWinINI);