The latest build for PHP 5.3/5.4 is currently here.
The installation steps should be somewhat like the following:
1. Download php_imagick_(ts|nts).dll from here and put it into your extension_dir. ts means thread-safe and nts is non-thread-safe. The latter is usually used with FastCGI.
2. Add the ImageMagick binary folder into your PATH
3. Restart just in case
4. Voila! You should now see imagick in phpinfo.
Obsolete builds: http://valokuva.org/magick