barrycaruth reports this:
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=182352#Post182352
 Code:
$result = WriteValue ("HKEY_CURRENT_USER\Software\Blah","TestValue","4294967295","REG_DWORD")

4.53 writes ffffffff
4.60 writes 7fffffff