Newbie- Here are some brand names that work well for the cyclist on a budget looking for a road bike: Raliegh, Giant, Fuji.
The key is to get a bike that will not hurt you. It is all about fit. I have short legs, and the Giant small frame worked for me better than any. I can honestly say I was tired after the double century Seattle to Portland last summer, but there was nothing about the bike itself that hurt me.
I am doing the same this fall, the MS150. We have a mountain bike MS challenge here too I have done before in June, probably doing it again this year. You could get away with a mountain bike ride on your Huffy, but it might break down in the middle of the ride.
This was my daughters experience on a church ride of sevreal days last summer. I got her a Kona asphalt bike ( the Aloha ), which is something you might consider, and hers was the only bike that did not break down.
I commute on a Trek multitrack 7300. This is a good solid bike sometimes called a "hybrid" and can be purchased new for somewhere between $300-$500. I saw a lot of these on Seattle to Portland. You will not break any speed records, but you will get there and the bike will hold up. Fit it with a rack and buy some painiers and you will be amazed how much you ride. Then after a while buy the road bike. The mutitrack is sturdy and the most versitle bike I own.