if it is a 1.7 dti then it has a cambelt which vauxhall recomend replacement every 100,000 miles or 10 yrs(which personally i wouldnt let go past 60,000 max) but if it is a 20dti then it has a timing chain which dosent normally need changing untill a noise develops to say there are problems. (chains can last for v v v long time as long as regular service intervals are followed.)