Luke I would recommend that you try contacting your web host's support team, and checking to see if they can install Smarty for you. If they can't, you can download the entire Smarty library and put it on the server yourself - you would then just need to change the paths in your code to refer to the local copy of Smarty(because the installed version wouldn't exist).
Luke If you're not using Smarty, I would highly recommend that you look into it, and fast - I don't think I've worked on a single PHP project that hasn't become large and unwieldy without some sort of template engine to keep the code and display logic separated.
checking to see if they can install Smarty for you. If they can't, you can
download the entire Smarty library and put it on the server yourself - you
would then just need to change the paths in your code to refer to the local
copy of Smarty(because the installed version wouldn't exist).