First off, please post more details regarding what PHP scripts you are running and wanting to run and how you wish to do so.
You need to create a new database for the new script, which as long as you do that, you shouldn't have any conflicts with it. And as far as adding a new script, just make sure you don't install it directly in the same folder as you have already installed the other.
For example, if you put your first script in your htdocs folder, then you would need to put your second one in a new sub-folder in htdocs. You can place it in a completely different location, but that will take more configuring than doing it in a sub-folder.
Post more details on what you're trying to do and someone will be able to better assist you.
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