Ok.
You probably will need an intermediate version of PHP to run about 97% of the scripts you need in PHP. Well the legit and unharmful ones. So you will want to apply for them in your AMP (account management panel). All the scripts on Fantastico (almost all) need PHP v2/Intermediate to work. Some need v3, and I'm not sure if any can work with v1 though. So go to your AMP and upgrade. I also suggest you manually install your scripts instead of using FANTASTICO, because like what tittat said, it's usually not up to date, and sometimes it has security holes in it, which can be dangerous to your site.
I don't suggest you apply for v3/Advanced unless you have a really good reason. As it's rarely accepted, and only two admins can give that level to you...