I also have the Encore N300 USB adapter, trying to get it to work with Backtrack. Thought I might give you some info that helped me out.
When searching for a driver I found out that this card uses a Realtek chipset (rtl8178 I think) that should be compatible with the rtl8192cu driver, which comes with Backtrack 5 r1 (the release I'm using). Well, I used modprobe to load it, saw it was successfully loaded with lsmod, but it wasn't recognized as an interface by either ifconfig or iwconfig, so I think perhaps it is not? Or is there something key between loading the drivers and registering the interface that I'm missing that's not allowing it to function? TIA for any suggestions, LQ.
I finally found my exact model number (its ENUWI-2XN45 btw) and consequentially, this page:
It says the latest Linux driver it has is for kernel 2.6.8 and earlier. Backtrack 5 uses 2.6.8, Backtrack 5 r1 uses kernel 2.6.9, and Backtrack 5 r2 uses kernel 3.2.6 (wowza) which seems to be the problem this guy is having:
I'm not sure what version of Backtrack 5 you are running, or what model your adapter is, but if yours is the same model as mine, I was curious as to what driver you are working with. You say you have a tar.gz, whereas the file I got from the Encore website is a .zip file (curious enough in itself). If you are on the original BT5, it should work fine for you, but I can not help you install it as I don't know the commands myself. I can't remember the command to extract a tarball at the moment either; I'm sure there are several guides for each of those that should be easy enough to find. I'm not sure what tutorial John is referencing though, that page doesn't have any walkthroughs for installing drivers or configuring wifi that I could find. The BT forums are a good place to find info tho, although they block registration from detected tor exit nodes. Slightly hypocritical in my opinion, but anyways.
The guy at the Backtrack forums doesn't say which model his adapter is either, but he says it uses the same 8192cu chipset, so perhaps it's the ENUWI-2XN45 as well. Either way, his driver has the same 2.6.8-and-earlier kernel support, so he has bigger problems than that as he is using r2. Although it looks like he went ahead & tried to use the driver anyways? Not something I would advise, or try myself. I will be going back to Backrack 5, there's not too much I'll miss from r1.
I'm afraid your problems are larger than that as well, as you are using a live USB version and I'm pretty sure that, unless you have a larger 16G or 32G with a persistent install config, you aren't going to be able to install, cuztomize, or configure ANYthing and have it carry over to the next bootup. I use a live USB version put together by the people at hackfromacave.com in addition to a HDD install, so I was hoping that the rtl8192cu driver would be compatible with this chipset since its already in the live version, and it would allow one to take not only a flash drive as well as an OS with you to other computers, but a wifi NIC as well. Hope some of that was helpful! Perhaps someone will post back with a simple fix for the rtl8192cu driver, but the cmds to get your driver installed/configd/running you should be able to search and figure out alright on your own I would think? Any linux software I've downloaded (aside from .deb's) has come with a README.txt or INSTALL.txt as John said, which has always had accurate instructions for me.