1. Throw the freshwater sand away
2. Set the tank and whisper filter in the sun for 2-3 days. Nothing that can harm your saltwater fish will survive this "burnoff".
3. Buy a 20 lb bag of live sand (about $20), 20-30 lbs of liverock (anywhere from $70-$200 depending on where you buy the rock and how much you pay), a bag of salt (maybe $20) a small powerhead ($20), a test kit ($30 for a good one), and 30 gallons of RO water from your lfs ($10-$15). Also buy a refractometer if you can find one. I'm assuming you had a heater for the 29 gallon already. The rock will be the most expensive part of this, but you will be able to move it to your big tank later, so it's not a waste.
4. Add the RO water to the tank.
5. Add the appropriate amount of salt to the tank (refer to label on bag).
6. Put powerhead and heater in water (set heater for 78-80 degrees f). Let circulate for 24 hours. (at this point you can use your refractometer or hydrometer to start testing your salinity - you should be aiming for about 1.025)
7. Add livesand. Wait until it settles.
8. Add liverock. If you are buying the liverock from an lfs (local fish store) I recommend waiting to buy it until your sand is settled and you are ready to put it in the tank. That way you can take it straight home and put it in the tank with minimal die-off.
9. Turn on filter.
10. You have about a month from this point to read as much as you can, play with your test kit, and obsess over what fish and corals you're going to buy!
I would personally skip step 7. I don't keep sand in my tanks, and if you plan to keep this tank as a QT tank later then you won't want sand in it. A lot of people will probably flame me for this little crash course, but I remember what it was like starting off. So I hope this helps you!