He dragged the .avi file into the window.

If you search for "K Lite Codec Pack Windows XP download," you will find dozens of scam sites offering fake "XP compatible" versions.

The desktop was a time capsule. A LimeWire icon. A folder of MP3s from 2005. And there, in the start menu: K-Lite Codec Pack .

His friend Marco, whose family had a T1 line, swore by one solution.

K-Lite Codec Pack handles local files only. For YouTube on Windows XP, you need a modified browser (like Mypal or New Moon) plus a legacy Flash/HTML5 decoder – that is a separate issue outside the codec pack.