Not sure how the dual-band works either, even though I have a dual-band router. How it works with the router is, it sets up each band under its own distinct wi-fi network ID. Unless there's something special with the dual band adapters, you'll only be able to connect to one network at a time, but at least with the 5GHz band, you'll generally have less outside signal interference. Other than that, it should be exactly the same as connecting a normal G- or N-band network adapter (a network card IS a network adapter) to your wi-fi network. As long as you can detect a network and have the security code, you should be able to connect.
Changing voltage on a fan is all done by your motherboard (unless you connect your fan to a fan controller). Some of them can do it (adjustable via bios or software control like Speedfan), some of them can't (hard-wired to only provide a constant voltage). "Changing voltage" is the same thing as "changing fan speed", and when you tell Speedfan to change a fan's speed, it tries to tell your motherboard to change the voltage going to that fan. Like I said, if your motherboard doesn't accept those signals, or has the voltage hard-wired, Speedfan won't do anything to your fan speed.
I haven't used Speedfan in a few years, so I can't offer too much advice on its use. From what I remember of the version I had before, it tries to auto-detect any fans you have and displays what speed they are set to, which you should be able to change. Now, if your motherboard doesn't support that kind of control, there's things you can do to change it in hardware. There's fan controllers, like I mentioned before, that plug into your computer's power supply. You then plug your fans into that and it provides speed control for your fans. There's lots of different kinds, brands, and complexities, but basically it comes down to how much control you want over reducing/controlling the voltage to your fans.
Speedfan itself is a pretty lightweight application, and settings/configuration are different for each model of motherboard. That said, it was pretty good about automatically configuring itself, from what I remember. If someone else uses it now, they could probably help you more with it than I could.