5k really isn't that far in the grand scheme of things and should only take about an hour tops and that's with walking. I have just started running in May and did my first 5k a couple weeks ago (in about 25 minutes). What I have learned:
1. Once you get past the first mile, it seems to get easier. Just keep running consistently.
2. Don't run with a cotton shirt, it will get soaked with sweat and get all heavy and clingy on you. Dryfit wicking stuff is awesome.
3. Keep your toenails cut really, really short--you'll only make that mistake once, trust me.
4. Get quality, well fitting shoes--paying special attention to any spots that rub on the top of your foot or toes.
As for the race:
1. Pace yourself.
2. Stay hydrated
I'm training for a marathon at the end of September and have run/walked 13.3 miles--my farthest distance and did a consistent run/jog of 11 miles. The more you do it the easier it gets to run. If you run outside on a road, make sure that you balance running on the left and right shoulder so you don't screw up your hips.
Good luck with your run.