Guess what? Yeah, looks like everything's all set.
But it was kind of strange. I started over from scratch on both computers. On the first computer, I did everything the same as before, then I cycled the power on the modem and it didn't seem to make a difference. I fiddled around for another five or ten minutes, tried connecting to the wireless, and it worked. I'm not really sure what happened.
The second computer was a little more annoying and it took over an hour to get it to work. I did the same thing as on the first computer, but nothing was working. After a little while, I discovered the firewall WAS on on that computer when I thought it was off. I turned it off, hoping that that was the cause of the problem, but nope. Finally, after another half hour of trying everything I think of, I decide to look at the IP address of the computer and I noticed that it had a static IP address. I set it to "Find an IP Address Automatically", tried again, and it worked. So much trouble for something so simple...
Thanks, everybody, for your help!