The easiest way would be: Create a trigger once in the place you want the level to end, then link this to a target_level_change (control+k links things). You can set the level change to load up one of the levels from JO, for example the first level is kejim_post
The more complex way of ending a level involves credits, for info on creating custom credits:
http://www.geocities.com/kengomaps/tutorials.html)
Doing this would require learning things from a few more of the tutorials there and would up the construction time of your map a fair bit, I leave it to you.
For future reference man, the showcase forum is for showcasing srceenshots and details of your projects. Of course asking for help in these threads isn't frowned upon, unless that is all the thread contains - in which case it should be in the mapping forum which you'll find nextdoor to this forum :)