Well, ndiswrapper is something I don't have a whole lot of experience with. What you did should work fine... you said you entered "nidwrapper". Did you mean "ndiswrapper"? That would solve problems.
Also, files go away it BT3 on restart because it's not persistent. I think the BT3/4 installers set up a persistent partition automatically. Basically, Backtrack is read-only. It loads everything it needs on boot into memory, then makes changes in memory as well. When you restart, it's gone. Creating persistence basically creates a file that holds all the changes you make. It's like telling BT, "when I create a file, don't stick it here -- write it to this filesystem". I have a USB drive with BT4 (formerly BT3), and when I boot from that it gives me several options, one of which is labelled somewhere as "persistent". Try that, it should keep all the changes you make.