The last time I was there, Alamo Car Rental was via shuttle- don't know if this is the way it is now, because the last time I was there was in 1997.
I don't know about an observation deck, but I do remember going to the 94th Aero Squadron Resturant, which has (is it still there?) a nice view of one of the runways (9R/27L?). There's also an awesome airline-themed resturant near the airport (I think it's at a Days Inn) which has models, memorabilia & you actually sit in airplane seats when you eat- I'd try to stop there. I have no idea what it's called, though, so I can't help you there.
A310/319/320/321/333, ARJ, BN2, B722/73S/733/734/735/73G/738/739/744/757/753/767/763/764/777, CR1/2/7/9, DH6, 328, EM2/ERJ/E70/E75/E90, F28/100, J31, L10/12/15, DC9/D93/D94/D95/M80/M88/M90/D10, SF3, SST