I've done a couple 1/2 marathons but can honestly say that I could not run a 5k without stopping. One day I hope to be able to but to be honest... I can't even jog a 1/2 mile without having to stop and walk.
Oh well... I guess. I have another 1/2 scheduled for February, I'm wanting to finish in 2h 30m but I don't see that happening.
It is addicting though, when I went to the expo for the last one in Sept, I signed up for 2 more.