xSiteable should run fine on any standard LAMP or WAMP stack.
Apache 2+ with the following modules:
IIS 7+ with the following modules:
Other webservers running PHP should work fine, but we do rely on some form of rewriting. If you know how to set that up in your environment, it shouldn't take you much to figure it out. However, feel free to ask on the mailing-list, and share your experiences.
PHP 5.3 or above, with the following modules:
It is possible that PHP 5.2+ might work, but let us know how you fare. We've set the PHP 5.3+ standard so we don't have to have a lot of code dealing with past PHP mistakes.
Other databases will most likely work, but haven't been tested, however xSiteable uses the basics from PDO and SQL and should be fairly compatible across most SQL databases.