Starting with version 1.0, you can uninstall programs and installed modules with make uninstall in the ndiswrapper directory. This won't remove the Windows drivers that are installed in /etc/ndiswrapper. For that you should use the ndiswrapper -e <driver> command. The rest of this document shouldn't be necessary in order to uninstall. If you have problems, however, follow it and see if make uninstall fails to remove anything.
Make sure you unload your current ndiswrapper module with modprobe -r ndiswrapper.
You need to remove the userspace tools ndiswrapper (in /usr/sbin) and loadndisdriver (in /sbin), and kernel module ndiswrapper (in /lib/modules/'uname -r'/misc), where 'uname -r' is the kernel number given by the output of the command uname -r. If these files are not in these locations, then they may have been installed elsewhere (e.g., userspace tools may be installed in /usr/bin). You can use which to know where the tools are located (e.g., which ndiswrapper gives the location of the ndiswrapper tool). Once these are located, remove them (e.g., rm -rf ndiswrapper). Note that the kernel module file is called ndiswrapper.o in 2.4 kernels, and ndiswrapper.ko in 2.6 kernels.
Alternately, you can use locate to find where the ndiswrapper files are stored. First, update the database used by locate with updatedb. This takes a while to run. When it is done, run locate ndiswrapper and remove all the files listed. Then run locate loadndisdriver and remove all the files listed.
If locate doesn't find the module, you can use find instead:
find /lib/modules/$(uname -r) -name "ndiswrapper*" -print
This will print the location of the modules. Remove all the files listed.
Ndiswrapper installs Windows drivers in the /etc/ndiswrapper directory. If you want to uninstall just a specific Windows driver, first list the drivers installed with ndiswrapper -l. If you then want to remove, say, driver "net8180", then remove it with ndiswrapper -e net8180. If that doesn't work, just remove the directory /etc/ndiswrapper/net8180 (e.g., rm -rf /etc/ndiswrapper/net8180). If you want to remove all the Windows drivers, then just remove the /etc/ndiswrapper directory (e.g., rm -rf /etc/ndiswrapper).