"The lecture is on that disk."
Translation:La prelego estas en tiu disko.
Even though prepositions are generally taken quite literal in Esperanto (in so far that is possible with prepositions — they are tricky in all languages I know!), I believe that "sur tiu disko" is a fine translation here.
Prelego is a difficult word to remember. Any ideas on how to remember it easier?
Legi means "to read"
"Pre" in English is kinda like "before".
So I remember "prelego" as the before-reading. Cause usually you sit through a lecture before reading the assignment XD (no matter if you were suppose to read the assignment prior to the lesson lol)
That's basically where it comes from, but the connection is in Latin (IIRC). It's a single root in Esperanto. German vor-lesen - to read forth. In the old days, professors would read their lectures forth to the class.