Looking for an unforgettable way to celebrate that special occasion? Well, the range of options open today's youngster - or even " oldster " for that matter, is a far cry from the traditional party or restaurant visit. No longer is it considered sufficient to invite yourfriends round, buy some food and get a barker to produce a cake. No, today's birthday boy or girl is looking for something out of the ordinary, ranging from the outrageously expensive to the downright dangerous. Anything goes, as long as it is unusual and impressive.