[Semaj Finks]"Does anyone out there have a PIP/Splitscreen preset for After Effects? Or does anyone know where I can find a good one?"
In After Effects, this is simple compositing. Just add another layer, and reposition, scale, and mask as necessary. If you need stroke or drop shadow effects on your PIP, you could use layer styles.
Is there a specific look you're trying to achieve?
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Curious as to why you would want a preset for that. It's one of the simplest operations you can perform in AE. Just scale down your layer.
Are you looking for some sort of stylized frame or border? If so, take a look in the AE Animation Presets.
Specifically, check out Inset Video-Framed