You probably need to turn off your firewall and/or antivirus.
Did you disable UAC when you installed XAMPP?
[ed. note: willyps last edited this post 11 years, 8 months ago.]
I had so many different problems with XAMPP on W7 I don't know which change fixed the package download problem, as I was not testing for that with each change. I eventually gave up on the other problems (not related to MODX) and installed a lamp server on a linux machine.
I'm not sure where's the problem. I tried newer xampp - same, xampp with installer for modx - same, wamp - same. Sadly I don't have a Linux machine, but may try on Windows server.
I got it working when I installed older Xampp - VC9 and PHP 5.4. On the newer VC11 PHP 5.5 and 5.6 versions the Apache server crashed sometimes, although I did try to run a few PHP frameworks there and they worked without a problem.