AjaxPages allows you to serve up full pages completely with ajax. This is very useful if you want to build a site that has a music player running across page loads, but don’t want to use frames. This technique can be found at TheSixtyOne.
All internal links should be in hash format. Example: instead of linking to filename.html, you would link to #/filename.html.
If you have clean urls on, the hash is almost not noticeable. Example: domain.com/#/profile/username
To get started with AjaxPages, get the files from the Google Code trunk. Example files are included. That should be enough to get you started. The plugin is very lightweight and fairly simple so it should not give you any problems.
If you need help, please leave a comment and I will personally help you out.