Mac Mini - just how hard is it to get Windows 7 on there and what am I looking at AFTER I get it on there....does it do everything that a Win based HTPC like the ASRock would do?
Extremely easy.
After you get OSX set up and logged in (which basically just means turn it on and tell it some stuff). You just open the Applications -> Utilities folder on your hard drive, and then launch the Boot Camp application. This will walk you through the steps. First it gives you a very simple disk partition dialog where you repartition the disk to make room for Windows. Then it downloads the "Boot Camp driver package" for Windows, and prompts you to save it onto a USB drive (or burn a CD). Then, lastly, it asks you to insert the Windows disc. You do, reboot, and then it installs Windows onto the partition you just set up.
From there, it'll boot into Windows. You insert the USB drive you made earlier, and install the Boot Camp drivers. This enables everything from Right-Clicking with your mouse (if you use the Apple-provided magic mouse), keyboard "volume control" and "track changing" support, and the Intel, video card, sound, etc drivers all in one go.
It also installs a Control Panel app that you can use to set the default boot OS (Windows or OSX), and configure the Keyboard and mouse support (so you can swap the F# keys for the "multimedia/hardware functions" by default), and all of that kind of stuff.
From there? If you set it to boot Windows by default, it IS a Windows box. And a nice one at that.
One tiny recommendation though... If you intend to use a Windows OS disc you burned yourself, you have to "do it right". Macs use EFI BIOS and don't boot right to some Windows install discs that are burned in some common ways. You can fix it with a little elbow grease if that's all you have though, just ask if you're in that situation. I can point you to a guide. BTW - This applies to many other Sandy Bridge Windows machines too now. It is an EFI thing, not a Mac thing.
If you use an "official" Windows disc, you won't have any issue.