I've been MIA this week too...reading all your posts but having nothing to share

Here's where I am at...
I am thinking about registering for my first 5k on December 5th (and I am already signed up for one on January 1st) but am worried about whether or not I can do it.
Now, I generally run 5K three times a week at home on my treadmill and, although I am running slowly, I can run it no problem. But I have NEVER run outside in real life. This week, I was determined to try because I need to start getting used to it if I am going to do these upcoming runs.
So...I've been totally psyching myself out and wimping out (it's cold...it's raining...whatever). So much so that I haven't run at all this week...not even on my treadmill! (Wha' the?)
So tonight...I finally went outside and started running. And it felt like I had never run before!! I couldn't find my groove, my breath was raspy and difficult, I didn't even make it a mile (in fact...closer to half) before I walked. Ug. I did only a mile and then gave up, picked up a friend and walked for four more.
What am I going to do? How do I make this transition? What am I doing wrong?
This just sucks. I am just feeling really discouraged with myself...
Is running outside REALLY that much different? I know it's cold and windy tonight but this seems crazy. I am still coughing like I did after my first 20 minute run during the C25K. Ugh.
Any words of wisdom?