I had this same problem on my last installation and it worked itself out while i was fiddling. i cannot for the life of me repeat whatever caused it to work...I broke my arch and had to re-install using the same iso (0.7.1).
the ndiswrapper version is 1.26
the modules that come with my default installation are all under /lib/modules/2.6.15-ARCH whilst the ndiswrapper.ko is being installed under /lib/modules/2.6.18-ARCH. because of this i get FATAL: module not found when modprobeing. simply moving the module to the proper directory does not work due to versioning complaints (is it possible to force the module, and if so should i?).
for at least the next 2 weeks, if i cant resolve this, i wont be able to run pacman -Syu on that machine. there is no way for me to connect to the internet other than my wireless so let me just say that command won't be helpful to me right now
my school is all wireless and my apartment only allows one laptop on their internet service per home and well...mine isn't it. i know this problem can be solved without updates as it was done before. Thanks!
i guess the ndiswrapper in /extra is newer than my version of arch, i just installed the wrapper from source i managed to grab. the package was nicely in that only a make install command was required. no special config files or options. only problem with this method, i imagine, is that now pacman has no info about the installation and will have to be manually maintained in the future...assuming of course an update doesn't fix the original problem.
The ndiswrapper in extra is indeed built for the 2.6.18 kernel as you have discovered.
Using abs/ makepkg you could build your own ndiswrapper package for the 2.6.15 kernel, but there is an easier way.
Use tpowa's new base iso along with the binaries from extra for ndiswrapper and ndiswrapper-utils.
The link points to a base iso with kernel 2.6.18 and packages updated to the 19-11 stand.
Booting with apg Openrc, NOT systemd.
Automounting : not needed, i prefer pmount
Aur helpers : makepkg + my own local repo === rarely need them