Ghent is on the same rail line that you take to Bruges (but not as far along), so you can get there very quickly. Take a direct train from the main Brussels rail station (i.e. the one where Eurostar arrives. It's known as either 'Midi' or 'Zuid', depending on which language the signs are in). The journey to Gent St Pieters station takes half an hour. There are at least two trains per hour, with most departures from Platform 15. (A few go from Platform 16).
http://www.visitgent.be/eCache/VGG/3/114.dmdfb GFuZz1FTg.html
Those trains from Platform 15 (or 16) usually go through to the coast.
Ostend is an absolute delight, with something for everyone. Almost every other building (especially by the fish quay) is a restaurant or bar, serving really good food. There's a great beach and loads of shopping opportunities. Some trains from Brussels go straight there. At other times yo need to change at Bruges. (The connecting service is always waiting there for you. The entire journey takes around 1� hours)
http://www.toerisme-oostende.be/index.phtml?la nguageid=3
Chris