For the Del Sol seats into a 92-95 Civic, it's pretty easy, but kind of time consuming for the first-timer. Took me about 45 minutes to swap rails the first time.
You just basically remove two bolts from each rail, the main time consumer is the fact that one of the bolts to remove is the one that holds on the side of the seat. Check out
THIS HOW TO on H-T. It's for an EK but the same principle applies.
S2000 seats are a much more involved project since you basically have to swap and reupholster the seat pans.