First DR trip - things to do?

i am not sure how much scuba diving you can do without certification. maybe a practice run in the pool? saona island is beautiful, i've also done parasailing in punta cana and two people can go up. one of the best experiences ever. Ziplining sounds cool and i didnt even know it was offered there. i hear dreams is a great place to stay too. enjoy! Look into getting malaria pills and travellers diahhrea meds....sometimes imodium and pepto doesn't cut it down there. I would get a Hep A and B vaccination just incase you haven't been vaccinated before. Also, take bug spray because there are sandfleas and if you are allergic to the bites (like myself) they will flare up into big welts. I only seem to get them in Jan/Feb though. Not the past 2 times when I went in November...but those two times I sprayed on heavy duty bug spray everytime i went to the beach so who knows if it was the bug spray that helped or time of year.

Have funnnnn!

Saona island is o.k., Zip line is great and nearby,
in case of meds i never recommend, that only should be done by your doctor, not by a travel bord, during my growing up in Gremany i received much more mosqu. bites than in my 13 years on the island, they are present but during our european hot-summer-nights they've been far much more painful. use the repellant you would use at home, i never use some myself.
in case of scuba diving without a certificate you can take a "quick course" with the hotel's diving center and afterwards they take you out to the diving sides, of course to beginners sides, not the pro's.
mountains and waterfalls are not the usual surroundings in the punta cana area.
have fun
Mike

what is ziplining and where can you do it?

About the mosquitos i have to disagree with MikeFisher. The mosquitos over there are killing me if im not carefull!! Although you dont need large amounts of spray and not during the whole day, but around 5/6 its horrible!! But if I put shoes and long pants around that time its alot better already. They seem to go for feet and legs mostly, not much arm/face action going on. Although I have to mind my lower back when im sitting so it doesnt show skin (they love that stretch of skin ) or put lotion on it there. And then im fine.
Sitting in wind or fan helps a lot too.

haha
Princesa,
looks like they like you more than me,
and sure i am not jellous, lol.
Mosquitos on daytime i know only from our Finca in the center of the island,
down here in PC my 2 hands are enough to count the daytime mosq's i see'feel per month. when the sun starts to go down is of cours ethe time they come out in their present numbers, but it really depends a lot at which location you are at that moment. like on the mentioned finca they would eat you alive, so i wear long sleeves and long jeans for sunset. here at home(Ocean front in Cabeza de Toro) we have the very most time a nice little breeze so i sit right now 7:30PM in shorts and without a shirt on the veranda, watch the ocean and work on nthe computer, not one "M" nearby til now, and the few bites i may get during some eve's do really not bother. people at resorts in PC are anyways in an area where "M's" and sorrily a lot of other wildlife get's killed by poisoning several times a week, not much around as long as you do not sit for sunset aside of one of the few mangroves/wet areas which are left since 'civilization' killed those areas.
it will be right away different if you stay at a area/house/location nearby some 'montes'(wild areas without constructions), there are always wet spots available and that's where those beasts grow up, so there they are present, but still, in 13 years i did not really got bothered by them.
a ventilator nearby is always a good idea to keep 'em off, on the finca we burn cocnuts in small metal cans to keep them off the area where we sit.
none in my family over here is using repellants/sprays or such.
have fun
Mike