To help those facing a common problem with phpMyAdmin, Stefan Mischook has created a video to show how to fix the "phpMyAdmin – Error Cannot load mysql extension" problem.
In a nutshell, PHP cannot find the library (mysql.dll - on Windows) it needs to connect to MySQL.
Fixing the problem is a (hopefully) simple four step process that he documents in the video. It's for Windows only, though, so those on other OSes will need to check out other sources.