About the best way to describe the differences between the two are that "Beverage Seminars" cover pure bottled product, which is usually wine, but could also be just about any spirit, beer, or tequila. "Mixology Seminars" usually cover blended beverages and cocktails that are made from various components.
In both cases, the format is basically the same. A representative (usually from the company or distributor behind the featured product) gives a presentation about the beverage, while two or three samples of the beverage are made available to each guest.
In the case of beverage and/or wine demos, the 3-4oz pours are already on the table as you enter the event space. For mixology demos, the samples are brought out as they are being discussed in the presentation (to keep the drinks as fresh and "just mixed" as possible). In both cases, water and a few club-style crackers are also available on the table. Often times, a pencil and small note card containing information about the beverages that you will be sampling are at each place setting. In the case of Mixology Seminars, the "recipe" for the mixed cocktails is also printed on the card.
For those that have been to wine samplings before, this really isn't a "vertical tasting" as many of the wines are of different varietals, but are on the same level.
Popular beverage seminars can be booked to capacity many weeks before the festival begins, so if you really want to attend a specific seminar, it's best to make reservations as quickly as possible. With that being said… Beverage and Mixology Seminars are easier to score last minute tickets to than the nearby Culinary Demos. Check with the Guest Services Kiosk at the entrance of the Festival Center (it's a little booth after you enter the building and walk down the winding ramp) for any last minute availabilities.