You can add a new page and then set the background in Properties -> Template
tab. You can select which template you want to use and also create an ad-hoc template which will be used only for the current page. If you do not want any content from the master page, set Inherit Content
option to Do not inherit any content
Details about creating a new page template can be found in Developer's Guide
I hope this will give you a brief summary of what you can achieve with page templates.