This has been covered a lot of times, about installing Backtrack on your HDD as the main OS or dual-boot.
Regarding your "uncertainty" about your wireless card check aircrack: http://www.aircrack-ng.org/doku.php?id=airdriver-ng also read their docs.
And your sections question has no answer:
This all depends on your knowledge, if you know which tutorial to follow and understand it, if you fail then erasing everything from your hdd might happen.Second, I was wondering what the chances are installing to my hdd will erase everything off of my hdd. I planned on following the tutorial on this site.
Thread closed. OP if you want to add something more, pm me and I will reopen it.