I've heard the version of High Voltage that's on Hybrid Theory EP and the one on Reanimation
and then I heard the one on FPATPF and I got confused.

What CD does this version apear on? It sounded like it was meant for Reanimation but it's way different. It does, however, explain why Chester's voice echos the word "sometimes" at the beggining but I'm still confused. :( Can someone clear this up for me?

It was released on the One Step Closer single.

The one Frat Party at the Pankake Festival is the High Voltage Remix (not H! VLTG3, just High Voltage Remix) and it's also found on Hybrid Theory SE.