instructions
This isn`t originally from me. I found out from ausmate and a few others, he was told by others too, so its a collective effort and more than one way to achieve it. This is my preferred way.....

Parts:

bar 1 rot: x:0.00 y:180.00 z:0.00
scale: x:0.75 y:0.75 z:0.75

bar 2 rot: x:0.00 y:0.00 z:0.00
scale: x:0.75 y:0.75 z:0.75

Fishtank glass Top:

rot: x:0.00 y:0.00 z:0.00
scale: x:0.28 y:1.00 z:2.60
Collidable: ON
Invisible: ON

Generic_cone:use Primitive hollow halfsphere

rot: x:180.00 y:0.00 z:0.00
scale: x:7.00 y:1.00 z:7.00
Script: Cached Web Image but no extra address entered, so it turns red

Diving Board:

scale: x:6.00 y:1.00 z:1.20
State: Sprite + Trigger and enter "Divingboard_ani"

How To:

Note: rotation was at the time I did it, yours may be different. So take this setting with a pinch of salt.

Take the first semi circular bar with the sizes from above and set it flat on the ground so the green chassis just touches the ground at that scale. Move it where you want, looks good on grass, maybe a path leading to it. Clone it and reverse the rotation so the two halves become one whole circle.

Get a piece of glass fish tank lid (the blue stuff) and scale as above. Lay it on top of the two halves of bar and make it collidable. Jump on top and make sure it sticks out all the way around, so you can walk all over the full perimeter of the circle. then jump off and one last check that its level with the very top of the bar/s. Now make the fish tank lid invisible in the state tab. Add a generic cone as per the scale above and rotate it so the pointed bit is pointing downward. Place and lower it so the colour of the flat top "just" clears the surface of the bar top, then drop it slightly below so the blue around the outer perimeter shows and only the colour of the cone is in the middle. Jump up again and do a walk test. Next change the colour of the cone by hopefully cheating. Setting it to a cached image and not putting in a new address used to leave it red, whereas setting the same and deleting the address, leaving no address in and further setting it as "Texture Unlit" made it white. So handy for either white or red steps without linking a texture image or in this case a red coloured trampoline with a blue perimeter edge. If this no longer works then just apply a texture in the normal way as a link, you may prefer it anyway.

Set a diving board up (as above) and set it as a trigger, approx same size as the fish tank lid and overhanging all the circle of the two bars. Lower it just above that of the fishtank lid so you trigger and bounce but don`t fall through the fish tank lid, which as we said is set to colidable. Just experiment with this till its set right and then test bounce everywhere on the trampoline. Make sure the trigger isn`t set to collidable or you will have problems. Once set, also make sure its invisible in the state tab.