algorithm - How to generate random level from a seed?

How would I go about using a random seed to generate a game level? The same seed should always generate the exact same level.

For this example it would be a Worms style level. So each level would have a theme (grasslands, snow etc), base terrain, different objects such as trees.

So where would I start to create this kind of level generator? What would be involved? What concepts does it use?

Bonus points for any any good links (bonus bonus points for anything related to how it was done in worms or similar).

Thanks.