it is likely you have an Index problem OR you may have to specify the 'installer file'
If a folder is specified (and its under the DocumentRoot) then the 'starter' or Index file must be listed in the Index directives (found in \xampp\apache\conf\httpd.conf)
# DirectoryIndex: sets the file that Apache will serve if a directory
# is requested.
DirectoryIndex index.php index.pl index.cgi index.asp index.shtml index.html index.htm \
default.php default.pl default.cgi default.asp default.shtml default.html default.htm \
home.php home.pl home.cgi home.asp home.shtml home.html home.htm
When you get an "Index of ...", it means Apache did not find a file in that list. The order does matter, so an index.php would trump an index.html in the default XAMPP installation. That's what drives you to the XAMPP Welcome page.
I know nothing about Magneto, so I can't guess what it should be doing. Many scripts have installers that have to be called to configure the script, often with names like 'setup.pl, install.php, 'installer.php', etc. Some times the installer is in a separate folder.
I hope this helps, even if it only clarifies things some.