According to this link the initial dredging work for the marina canal started in 1998 and the construction of the skyscrapers started in 2002. I suggest checking out Google Earth. Search for "Dubai Marina" and then choose the option "View --> Historic Material". There you can see satellite pics from as early as June 6th 2003. They show the completed canal and some basic structures of the first high-rises. Now change the view to April 2nd 2010 and you will know what I mean.
Actually, this applies to most parts of Dubai... It was, and still is, one of the biggest construction sites on the planet. Sources have it that at one point a third of all the construction cranes available wordwide were in Dubai. Even today much of the skyline looks like a forest of construction cranes
Impressive! I've got to say, it's an amazing job this beautiful steel jungle they've built from scratch, but in the end what happens when they run out of oil? They've got to search for other income sources to keep spending and building crazy like this, which is kinda of difficult.
Dubai never had much oil in the first place, they are supported by Abu Dhabi. However, als these constructions are happening BECAUSE the region will run out of oil eventually. Dubai has always been a perfect trading and travel hub, located half way between Europe and Asia. That is a big assett and they are investing in the infrastructure in order to attract foreign companies - which works very well. All multinational corporations have an office in Dubai. Especially trading and the financial sector find very good conditions and a perfect infrastructure in Dubai. I believe Dubai is still just putting itself on the world map and will prosper for many decades to come.