Windows 5.1 Service pak 2 = Windows XP SP2
Local Host is always referred to as simply localhost
I have changed the topic title to a more meaningful subject
Is Apache and MySQL running?
Try using the new version 3 control panel found in the xampp folder after first clicking on the Exit button in version 2.5...xampp-control-3-beta.exe
...it has more features and a more informative log window and it creates a log file in the xampp folder after it is started for the first time.
Latest version can be found and downloaded from here:viewtopic.php?f=16&t=48932
You are typing http://localhost
in your browser?
What are "General settings"?
You have disabled the Windows default web server IIS?
What does the error.log file in the xampp\apache\logs folder give as a clue?