Your running for a good cause, which will help you through the training and help you run the race. If it helps I took up running for the very first time last Oct 09 after over thirty years of smoking and I love it cant think why I never took it up before, I have my first half-marathon in Sept.
Jacky if I can run then believe me your have no problem lol, I started running in Oct 09 after over 30 years of smoking and as Brian rightly says you do need a goal to keep you going, I did my first 5k in Dec 09 in 31 mins, when I got my medal I was on cloud nine as I've never ran anywhere in my life .
I'm doing a 10k race in April and a half marothone in Sept. I can now run without stopping for 1:45mins, which I'm over the moon about.
So if an old couch potato like me can do it then anyone can. As already said pick a 5k beginners training schedule and your breeze you first 5k race.
I enjoy running in the morning as theres less traffic and its more peaceful, for those cold winter mornings I run in my skins(thats compression leggings & a compression long sleeve top) and a running jacket and I also wear gloves, as already stated it doesnt take long to warm up.