Well first off, probably best to not buy anything at Fry's electronics, at least not until you've done a fair amount of reading up on things here.
The Freq numbers you're referring to are the range the HP can produce and you're right the first number is bass the second treble, but you can pretty much ignore these numbers since they tell you almost nothing about the quality of the headphone or how good they sound.
You can learn about the science behind each of the specs, but you'll find that they won't really help you that much when you're on the lower end. Frequency Response charts will help you much more than the specs on the box, but those too will take awhile to learn what they mean. I'd suggest reading reviews and then trying to get out an listen to some of the HPs that review well. At this point you probably don't know what kind of sound you like (bass heavy, treble heavy, V shaped, Mid centric, neutral, etc.) so you can't make a "perfect" choice based just on reviews and specs . . . you have to listen to them.
To really help you people need to know what your budget is and what kind of music you like.
As far as amps go, in general, don't worry about an amp unless you buy headphones that require more power than what your source (computer, ipod, etc.) can provide. If you're looking to spend less than $300 on headphones than don't worry about an amp at this point. Some expensive headphones don't require an amp, but in general the expensive cans need more power than an iPod has.
Try doing some searches based on your music preferences and budget, I'm sure there are at least 37 threads here that will answer your questions. I'm not saying you shouldn't post your questions, but I wouldn't look for any quick answers to what headphones you should get. Take your time and I'm sure you'll get a great pair.
Sorry I didn't answer the most of your questions, I just don't think they'll actually help you as much as you think at this point.