I'm all for not getting mad at people for not searching or RTFM first. I work on TFM a lot, and I know how easy it is to miss stuff there.
I'm just busting your chops, gates78 :D
It can be overwhelming with all the information (and misinformation) out there. We do get these questions an awful lot, though.
Like DrowningApe said, Pivos XIOS DS is a very safe bet, and a very good box. It's either the same price as a g-box or it's not a whole lot more, and has better support. Full disclosure, Pivos is a Team XBMC sponsor and they've hired two XBMC developers to work on the Pivos XIOS, but it's kind of that fact that makes them so well supported right now. I personally don't get any money from them (they are giving me an XIOS for XBMC related stuff, but as cool as it is, I have unused HTPCs right now), but totally recommend it since I personally know the guys working on it are really good at their jobs.
If you're not afraid to tinker or make/buy a separate case, the ODROID-U2 is about the same price and is a MONSTER of an Android device. Raw power, mmmm. It's pretty much just the exposed "motherboard" and no case, remote, etc, but like I said, if you like to tinker with stuff, it's a great option too. It also has enough power to software decode 1080P videos if overclocked, which means you have extra insurance that it will work smoothly with various videos, to put it simply.
I've heard mixed results for the g-box itself, but if you look around here and in the Hardware Forum section, you'll find a lot of people who give their personal accounts of using them.
For installing and most other questions, check out the
Android FAQ (wiki). If you have any more questions or need anything clarified, feel free to ask us. We might be cranky sometimes, but most likely we'll help you :D
