I did my first MS150 last year in Dallas. It was a great experience! It was a great challenge mentally and physically so start training now. But it's amazing how much and how far a positive mental attitude will get you!
I'd suggest a good pair of cycling shorts and a tube of Butt Butter because the chaffing on the inner thighs by the groing hurt me more than the mileage! Ugh!
I bought my first road bike in Feb of last year and rode the MS ride in May. We rode every weekend including 25-30mile loops and a few 62-65 mile oragnized rides to build up our miles. I felt that if I could do 65 miles, an extra 10-15 more wouldn't kill me. During the week we ate, well... better than usual, and jumped on the bike trainer 2-3 times during the weekday. The CTS and Spinerval dvd's were really helpful and still are. I bought the best one I could afford and it came with the CTS Time Trial dvd. It helped a lot. I also lifter some weights and strengthened the core muscles. I actually went from 180lbs down to 163lbs by the MS ride.
The main thing, though, is getting lot of miles under your belt. Or as many as you can get. Because believe me... for a first timer, it wasn't a cake walk!! And with good training going into day 2 wasn't that bad. You just need to prepare yourself mentally and drink lots of water during the week and during the ride. I used the mantra: " I will not be beat!" to get me through the hard times.
Here is my blog of the training we did for the MS Ride so you get an idea of what we did:
http://garylee333.blogs.friendster.com/my_blog/
Good luck! It was certainly tough but worth it. Moreso because I rode for a freind who had MS. So instead of just challenging ourselves it became very personal.
So now I'm training for the MS Ride (Waves to Wine) in San Francisco since I moved out of Texas. I was told that this year's ride is going to be really good including a start over the Golden Gate bridge down to Sausalito, over parts of the Tour of California route and so on. The hard parts... A month ago I was back up to 180 and I was told there will be 7000 ft of climbing on the first day. Good thing it's in September so I have time to get back into biking shape (not this round shape I've become!).
Oh yeah, there will be all kinds of people in all kinds of shapes and sizes so don't worry about going slow. Just go at your own pace and stop to eat sensibly and drink a lot.