From Jomres v4 manual

Requirements

Minimum Requirements

You must already have a working installation of a CMS to install Jomres onto. Jomres by default supports Joomla 1.5, however it can be configured to work on other CMSs, please see the article Customising Jomres to work on other CMSs.

• PHP 5.2.x or above
• MySQL 4.1 or above
• Apache 1.13.19 or above
• GD needs to be enabled.

Please note that Jomres does not work on Joomla 1.0.x, as it is no longer supported by the Joomla project. If you would like to use Joomla 1.0.x please see the article Customising Jomres to work on other CMSs.

PHP Requirements

To use the full functionality of Jomres you will need the following PHP features/modules enabled:

• CURL - Used for downloading all plugins including modules from the Jomres servers.
• File system functions - Used for uploading of property and room images, writing temporary data etc. (required)
• Calendar functionality - ( the 'gregoriantojd' function). PHP needs to be built --with-calendar to function properly. (required)
• You must ensure that you have MySQL, XML and Zlib support built into PHP. (required)
• You need to ensure that safe mode is off.

Whilst this list may look pretty daunting, most quality hosts will provide this functionality in a standard hosting package.