Don't worry about it, it'll happen when it happens. My ds started walking with help when he was 18 months. He went from crawling to walking holding onto furniture to walking almost on his own in the space of 6 weeks.
You hear of some children who are walking by their first birthday (apparently I was one) and others who still aren't by their second. If you're worried talk to your health visitor but by and large I'd say there is no hard and fast rule for when they should be walking and it depends on the individual child.
Also bear in mind that when they do start walking you have to bolt everything down or put everything 6ft off the ground that you don't want handprints on, ie photos, video recorders, valuable faberge eggs etc.