besides roasting, is there any other way to cook these please?

yes, doman1, yams can be cooked in other ways - here's some info from:-
http://www.vegetables.co.nz/vegetable. php? id=67

"ways to eat this vegetable... . .
As a side vegetable yams are great baked or microwaved with a little lemon juice, butter and a sprinkling of brown sugar. Yams are good roasted or added to potato wedges. They are also able to be steamed or boiled and can be served whole or mashed. A yam cooked for 40 - 50 seconds in the microwave makes a good snack for small children. Sliced yams are great in stir-fries, especially if still slightly crisp. Lightly cooked and sliced with a lemon or lime vinaigrette dressing makes a great salad base. The natural sweetness of the yams makes them really good to use with ginger, orange or sweet and sour type sauces. "

For a few more ideas (and recipes) have a look at:-

http://trademecooks.net.nz/viewtopic. php? f=23&t=535

thank you sam

http://www.halfords.co.nz/index. php? page=shop/article_catego
ry_results&article_category=82756c3bb8bb0954284227fabf76
02c9&PHPSESSID=ctbe6b2e5d69ntcb99koepokq5

Here some great ideas from a yam grower