dsk is right, the youtube beta in the video centre is the correct way of accessing youtube content for the time being. There is another thing to keep an eye on though,
If you open up the web browser, scroll down to the bottom, you should see a bookmark called 'Nokia video links' this will give you access to loads of video content from Rocketboom and Reuters and others, and eventually the YouTube service, you can try clicking on it now but it says page unavailable so keep an eye out for it we'll be sure to let you know on the WOM World when the service is fully up and running.