When I google for "Microsoft loopback adapter", I get

http://www.microsoft.com/technet/prodtechnol/virtualserver/2005/proddocs/vs_oper
ate_ht_install_loopback.mspx?mfr=true

   - Oliver

It does sound reasonable, but on my system NetBeans launches
applications through Tomcat as "localhost," not any IP address.

If the loopback adapter idea doesn't work, you might want to check that
your HOSTS file is set up correctly.  "localhost" should resolve to
127.0.0.1.  If not, add that entry. (HOSTS is in the WINNT directory,
under drivers\etc, iirc.)

Otherwise, check Tomcat itself can come up, outside of NetBeans.  Try it
from the command line, and as a service under Windows (from the GUI).
Check what NetBeans is is trying to launch, and make sure you can
resolve that manually also (localhost, 127.0.0.1, or whatever).  You
might want to check the NetBeans config to see what it is trying to do.

If none of these work, find the relavent console output under NetBeans
and any relevant Tomcat logs, and post 'em up, and we'll have another go.

The loopback adapter is part of Windows XP. The Microsoft Knowledge
Base shows, how to install it:

http://support.microsoft.com/default.aspx?scid=kb;de;839013