I know a lot of bride, myself included, have had a dessert party. I had mine at the Uk lower terrace/loch. There is a food and beverage minimum ($20 according to last years prices) to host the party. Most brides have desserts like cookies, brownies, or fondue. I believe one bride had her party as a cocktail hour, and served hors d'oeuvres. Basic tea and coffee comes with most dessert packages. They also have extra drink packages for the party. You can do something simple like soda, or have alcoholic beverages.
There are several areas around the WS you can have your party. It really depends on the amount of people you are having. Places like Morocco and UK are the smallest guest minimums, while Italy Isola has the highest. Other locations are in France and I believe Japan.
Some of the extra costs will come in paying for attendants, also you will need to pay an illuminations viewing fee if your guests are not planning on using a park ticket that day ($12.50 per person). The rental fee is $250 (depending on location and again 2007 prices) on top of the minimums as well.
Epcot has some basic high bar tables with linens (black or white) and chairs (green plastic chairs) that are available with the rental fee. You can upgrade to other linens, centerpieces, chairs, etc. if you choose to for an additional price.
I would call DFTW to find out where to start making this reservation. I don't know where else you could start to do this at.