I DL'd a splash pack, some I'd like to delete but how do I identify them outside of the game?

They're in Data Files\Spalsh folder, and are in .TGA format, so you might need appropriate program to view them.

Also take attention to additional splashes, based on Bethesda wallpapers. We, in Russia use them many years. Also they included in russian Morrowind patch.
http://hamster.rumor.ru/page2.html
Look to end of page.