I just got off the phone with Central Reservations. The CM said that the trundle bed at Riverside only fits children up to age 9. Since my younger son will be 12 this winter, I went with the two connecting rooms at Pop Century. I really did want to have a hot tub but saving (at 2007 rates) $132/night before adding taxes goes a long, long ways towards making this vacation possible.
For anyone else doing this - if you want to pay only the deposit on the lower priced ressie, you'll have to cancel the first reservation and make a new reservation for the lower priced room. Otherwise, they're happy to apply the higher deposit amount to your new reservation. And personally, I'd like to keep the money until February!
NHWX