What is this challenge about?? i know its the couch to 5k.. but whats the whole deal?? is there a thread about it???

any other challenges?? i want something that gives me a clear exercise goal...

There are LOTS of other threads about it. You should also check out the 100 push up challenge and the 200 sit up challenge!

There are some websites on it, this explains the entire program:
http://www.coolrunning.com/engine/2/2_3/181.shtml