CSS sprites are a way to reduce the number of HTTP requests made for image resources referenced by your site. Images are combined into one larger image at defined X and Y coorindates. Having assigned this generated image to relevant page

CMS Market (www.cmsmarket.com) has officially opened its doors to Authors! If you have a template or extension, add it to our directory and get immediate exposure! CMS Market offers much higher commissions than all the other template resellers, and also offers a marketplace for extensions!

Legacy mode is actually a Joomla! system plugin. It allows you to use extensions that were written for Joomla! 1.0.x (and even Mambo) in you 1.5 site. It is a part of the core distribution of Joomla!, but it is disabled by default. It is said to offer over 90% backwards compatibility. There seems to be some misunderstanding in the Joomla! community about legacy mode.