I love Ostend. It's packed with great bars and restaurants and there's a really vibrant atmosphere about the place.
Many of the best restaurants are by the harbour. (The bars are simply everywhere!). Ostend is a shop-a-holics paradise with everything from cheap seaside 'tat' to classy designer clothing widely available.
While Ostend has plenty to keep you occupied all weekend, it's easy to get to lots of other interesting places. The coastal tram line serves several other resorts, both large and small. (I like Blankenberge). However, the real jewel is the beautiful city of Brugge (Bruges), which is less than twenty minutes away by train.
The official tourism website is here:
http://www.toerisme-oostende.be/index.phtml?la nguageid=3
Unfortunately the racetrack (Wellingtonrenbaaan) only operates from July to September but you'll still find plenty to do. (If the sun's shining, you might just want to spend time on the beach. The sand is great and swimming is very safe, due both to the very gentle slope of the beach and the diligence of the the lifeguards).
Chris