According to the man page for Win32::TieRegistry (here), you should be able to do something as simple as this:

$Registry->{$key} = 'foo';

You might want to check your rights to that key too, since you're running under Windows XP. Also, try using 'CUser' instead of 'HKEY_CURRENT_USER' for the root key, there's something in the man page about that too.

The Secret to Fortune Cookies in One Line
print join("... in bed", `fortune fortunes` =~ m/^(.*)(\.|\?|\!)$/), "\n";