Your careers adviser at school/college/uni (or your local careers office) should have some examples of psychometric tests you can have (you might have to pay a nominal fee for them, about 20p or so per paper). Or you could be cheeky and phone up some of the bigger companies that use these kind of tests (e.g. IBM and Esso do, particularly for graduate-entry level posts) and see if they can send you some examples.