SureAI

So I'm thinking of running Enderal on my old PC (so as not to mess up my Skyrim install on my main rig.) The old laptop has a Core 2 Quad and a GTX 280M. This can run Skyrim at high settings and 1280x800 resolution with a performance friendly ENB and get about 40 fps. Would this run Enderal, or does the mod add too many textures/lighting effects/geometry/etc. for this old laptop to handle?

You could try it but Enderal needs more power than Skyrim.
You can look up the system requirements on this site.

If you want to play on your main PC: no problem at all. The Enderal launcher creates a backup of your current Skyrim files (everything except ini and saves). You can restore them through the launcher after you have uninstalled Enderal.
To be safe you could rename your current Skyrim directory. Install a clean Skyrim version. Install Enderal. If you uninstall Enderal again. You can just rename your normal Skyrim installation back to "Skyrim".
installation guide for Enderal
Installation gallery