XF 1.5 How to include php/html file

So, in the past on just general php sites i could use <? php include=..> wherever I wanted to display another page, its nothing special, but I hate iFrames, so that was my old workaround. Is there a better way to do this? I basically just want to include a small 'online users' list from a game server I run in the sidebar. I was going to just modify the 'share page' template, and I know I did it a year ago with jQuery, but cannot remember for the life of me how I did it. Anyone have any suggestions? It needs to be controlled by template, so I can get colors proper.