Beijing 2008

If you have 4 controllers and you find a friend that has 4 controllers aswell, you can boost this achievement easily. It takes a while, but its a lot easier than doing it against the computer.

Go to Competition > XBL Player match, sign all controllers (Apart from your main one) in as guests then invite your mate. Tell him to do the same and your ready to go.

Just make sure your player gets a score on the board for all events and then with the other controllers you dont have to get a score, just let their jump/throw etc be a foul. Using this method you will always win therefore earning yourself the achievement.

As I said this will take a while, probably about an hour+ for each person. The same can be done with the Heptathlon event

There is another method that will shave off a considerable amount of time.

MueKE and i were in a session using the 4 controller method when we were having connection issues during the long jump (2nd event). It would disconnect us during the event. So after 4 failed attempts we decided to test out winning only the 100m (1st event). Too our surprise it worked! After 10 wins the achievement popped.

The way we set it up was when i was to win the event 10 times MueKE was the host so he would quit out at the start of the next event (when the first player is about to start) and vice versa.

This way you will skip all events that require you to foul out all the guest accounts which saves a considerable amount of time. This method may work with the heptathlon heroine as well but is not confirmed.

UPDATE: It has been confirmed by midniteDLITE that this method does also work for heptathlon heroine.

This is one of the hardest achievements to get in Beijing. However it is very doable you just have to know which events can be problematic.

Obviously don't even attempt this until you have the achievements for each of the 10 individual events.

Once you have you just need to keep trying, the AI can throw up some real challenges in the 100M, Long Jump and 110M Hurdles. However, the AI appears to be random so you just need to keep trying untill you get poor competition on these events. The other 7 events are easy to win.

Just to add to those 2 solutions here is a list of all the events in the decatholon.
110m hurdles, high jump, shot put, 400m, long jump, javelin, 1500m, 100m, pole vault & discus.

I used eLiTeMC251's solution and it worked great but just to add to it so your boosting session goes faster, once you finish your 10 wins for the decathlon switch right over to the heptathlon and get 1 more win. You will receive the achievement for the decathlon and heptathlon after only 11 wins instead of 17.