EDIT: this stuff is mostly root-stuff, so either su - to root or use sudo to run the commands below..
Check what wireless-related modules you have loaded. You should have 'ndiswrapper' if it was installed OK, you should not have 'bcm43xx' and alike, or if you do, you need to blacklist them (which means, that the module is not loaded during boot process). If the bcm43xx module (for example) is built right into the kernel, and not as a separate module, then you can't obviously blacklist it, because it's not loaded (as a module) separately but is there all the time. In that case you need to 1) obtain a kernel that doesn't have it built directly into the kernel, or 2) rebuild your kernel yourself and remove that kernel module, or compile it as a separate module.
Blacklisting a module, let's say bcm43xx, happens by adding a blacklist line into the module configuration's blacklist file. The filename may depend on your system; I'm showing an example on how it's done on Slackware. You can safely try this, but if it doesn't work, it just means your filename is wrong (and you should dig a bit to find the right one out).
echo blacklist bcm43xx >> /etc/modprobe.d/blacklist
That appends a new line to the blacklist file, that says "blacklist bcm43xx". Effect is that the listed module is not loaded during boot. This affects next reboot obviously, and the effect is the same as if you do right now
as root. If rmmod doesn't work (for example there is no module bcm43xx installed), then blacklisting the module is not needed.
NDISwrapper installation must first be done correctly. Module 'ndiswrapper' needs to be loaded (set it to be loaded at boot). A reboot is usually required after installing NDISwrapper, because otherwise the card may not function properly. If there are several drivers, it may be that your ndiswrapper driver doesn't work; in this case the other drivers (modules) need to be removed first; this is what blacklisting is for (for kernel modules that are loaded during boot; for builtin kernel modules a kernel reconfiguration is needed). The native driver for Broadcom 43xx cards is called 'bcm43xx', I'm not aware of any 'b43' driver, but if that's some driver for the card, then you'll have to get rid of it so it won't interfere with your NDISwrapper driver.
For the first time I did this it was a bit difficult. But after some installs it has come more clear how the process works, and now it's easy; just have one driver and have it be ndiswrapper driver - and make sure ndiswrapper (and a right Windows driver) is installed without problems. There may or may not be a wireless device wlan0 or eth1 (doesn't matter at all which one, as far as you know what it is) before installing NDISwrapper driver, but if the native driver does not work, it's no good for you.
FWcutter works for bcm43xx cards, or so it's said. Never tried myself; I surely would have if I had met FWcutter before NDISwrapper, but this is just how it happened to go..the best way to get these cards working with NDISwrapper is to take it easy, slow and carefully.
1) Get right Windows drivers (a .inf and a .sys file)
2) Install the ndiswrapper and ndiswrapper-utils packages, if they are separate ones; for example Ubuntu comes with ndiswrapper, but ndiswrapper-utils is curiously enough missing and has to be installed separately (last time I checked, anyway). Also on the second newest Ubuntu version one had to make sure ndiswrapper-utils-1.8 was installed, not just ndiswrapper-utils; wrong version caused it not to work. Life is fun, isn't it?
3) rmmod any other kernel modules for your card, or reconfigure your kernel to get rid of them
4) Install the Windows driver with NDISwrapper, use ndiswrapper -l to make sure it's loaded and hardware is present, after this run ndiswrapper -m
5) Make sure ndiswrapper module is loaded when you boot, and that any other offending modules are blacklisted or removed from kernel. Reboot to make sure the module hassle goes all right. Try to enable your wireless card - do you get a sign (maybe a light somewhere?) that it's up? If yes, try to run
as root, or if you're one of those who have aliased to wlan0, use it instead. Should give some results, or at least not an error...
EDIT: it's really not that difficult if you think it as a whole. A driver is a kernel module. The native driver, if it exists, doesn't work, right? Then we shouldn't use it, because it's of no use, but can cause trouble. On the other hand, the preferred driver is the Windows driver (not preferred really, but there's no choice!) - since it's not a Linux driver, we need something to "wrap it up" for Linux. So we use this handy piece of software called ndiswrapper to wrap the Windows driver into a package that is then loaded to the kernel (ndiswrapper module is loaded, and ndiswrapper deals with the Windows driver - wrapping, get it?). So: native driver out, ndiswrapper in. Easy as that.