I found the best bet was to peruse our local bike shop(s). Hopefully you have one within a reasonable drive of where you are.
Justin and I were in the same boat earlier this year when we shopped for and purchased our mountain bikes -- it'd been over 15 years since either of us had done any biking or owned our own bikes. The first thing that will surprise you is just how light even the standard (Walmart, Academy, etc.) bikes are nowadays and how sturdy they are put together (terrific welds, etc.) Obviously, more expensive bikes are even lighter (Carbon Fiber), but most of us don't need to even consider those models.
After checking out bikes at two local bike shops and online, Justin and I both purchased
Gary Fisher Tassajara's. We *LOVE* them and they are built solid and a good value for the money (imho).
I still don't know all the lingo, since we learned only what we needed to in the process of locating and purchasing our bikes. There are some good online guides on the various bicycling magazines and enthusiast websites.
Make sure you get the right frame size for your body and build, and make sure to get a comfortable seat if that is an issue (we both ended up buying "anatomically friendly" seats for our respective bikes within the first month of use). Seat height is crucial as well, not only to keep from punishing your knees but also to prevent poor posture that will cause back and wrist/shoulder pains. Any decent bike shop will let you sit on their models and, hopefully, let you take it for a spin outside to see if it suits you. That's exactly what we did with our bikes and that really helped us determine which frame styles/sizes were best for our needs.
I'd never heard of Gary Fisher before we bought our bikes, but Justin had and Gary Fisher's actually been around for ages. I can now say from experience that they do make very good bikes.
If you have a BikeWorld anywhere near you I highly recommend them. I think they have a couple stores outside of San Antonio and they've always been terrific to deal with, including free routine maintenance on the bikes for the first year and free adjustments (seat, handlebars, etc.) Their prices on other services and basic merchandise are good as well -- they charged me something ridiculously cheap to repair two flat tires (suffered them in the same week -- one was my fault, as I ran over a cactus trying to avoid a fall on our first trip out; the other was a fluke -- something must've gotten my tire on a long road ride.) They've given great advice on local riding areas to check out for our skill levels (newbies) and we've even bought some apparel there though I recommend REI online for that generally after you have a sense for what fits you (I have an issue with the way they size most women's biking apparel -- I've lost weight over the past year, and was never really overweight, but I still find most women's bike shorts were made with Paris Hilton or Angelina Jolie in mind (both with figures far slimmer than my bones would ever allow, and with midriffs they don't mind advertising to the world because that's part of how they make their money.
If I can help in any way, let me know. I love love love mountain biking and enjoy a little road biking on our MTBs as well. It's been a terrific rehab activity for my knee after last February's ACL reconstruction and meniscus repair/removal (partial).