WordPress 2.5 (or higher)

PHP 4.3 or higher (including PHP 5)

PHP's XML extension (enabled by default)

PHP's PCRE extension (enabled by default)

Ability to change file/folder permissions (dependent on how much access your host provides),

Both PHP's multibyte string extension AND iconv extension.

PHP's cURL extension (disabled by default)

PHP's Zlib extension (disabled by default)