I am 5'8 1/2 and ride a medium in most 29er's, it all depends on your body build and the bike frame geometry. So yes there are plenty of 29er options for you. I would not buy any size bike without riding it first if you could. A small may actually be too small for you.
are the wheels on a road bike too big for you? 29" mountain bike wheels are the same size as a road bike wheel (700cc). 29ers aren't too big for you, if the bike is comfortable, it's good. get the right size frame, THAT is important. taller guys such as yourself are more comfortable on 29" wheels, so you should be fine.
instead of wondering if you can fit on a 29er or not, why not ask if the type of riding you do is right for the wheel size? I have a 29er and a 26" bike. the 29er sits most of the time as a backup bike or waiting for the course that is fast and flowing which isn't what I do most of the time.
29" mountain bike wheels are the same size as a road bike wheel (700cc).
The rims are the same size - 622 ETRTO, but the overall diameter of the combined rim and tire are very different. A 700c X 23 road tire mounted on a 700c rim is almost identical to the diameter of a 26 X 2.1 MTB wheel/tire (about 26.4").
A "29er" 2.1 tire on a 700c rim measures about 28.5" in diameter.
Arch, I am a hair over 5'9" and I have an 18" Jamis Durango 29. I've had it since April and so far, so good. I bought it after having been out of biking for many a year, and honestly, I thought I'd be doing a lot tamer riding than I currently do. So in hindsight, I may have been better served by a 26" trail bike. That said, I still like the bike quite a bit. As other posters have noted, try to find out the type of riding you want to do, and try to figure out what type of bike suits that style best. Above all, make sure it fits. It may be a good idea to get an inexpensive bike on craigslist, borrow one from a friend, etc... in order to ride for a while, and then upgrade when you have a better idea of what your needs are. As an inexperienced rider, it will be hard to figure out whether a bike works for you in the parking lot of the lbs. Best of luck with your decision. Keep us posted on what direction you go in.
I'm 5'9 and got a 19 inch 29er a year ago. Fit is almost spot on. I bought it online. I compared it (tt length) to my 'cross bike. I installed drop bars the day it arrived. I have to reach further for the brake levers and I can do so without locking out the elbows.
When I find some flat bars and levers I like, I'll give those a shot. This is a 'low budget' bike with inexpensive parts on it. I'm not looking at putting a lot of money into it.