I use GNU tar on Windows to tar my CPAN distros. It has given me no trouble. (My latest tarball upload to CPAN was about 30 hours ago.) Here's the output of my 'tar --version':

tar (GNU tar) 1.13.19
Copyright 2001 Free Software Foundation, Inc.
This program comes with NO WARRANTY, to the extent permitted by law.
You may redistribute it under the terms of the GNU General Public Lice
+nse;
see the file named COPYING for details.
Written by John Gilmore and Jay Fenlason.
[download]

Cheers,
Rob