WordPress Plugin Authoring question about jquery and css

One point for using wp_enqueue_script is for that very reason. Never assume anything, enqueue jQuery so that if it is there already it does nothing, but if not , it will queue it up.

If your talking about the image path for your plugin, you can use the following, http://codex.wordpress.org/Determining_Plugin_and_Content_Directories

The examples for plugins_url should help.