I may have spoken a bit too soon when I said that Madwifi worked. It's certainly an improvement on what I had before, but my wifi still has an annoying habit of losing the connection, and the only way I can get it back is to reboot.
I've tried Zuperman1's solution, but on entering the command
sudo modprobe acer-wmi
WARNING: All config files need .conf: /etc/modprobe.d/ndiswrapper, it will be ignored in a future release.
WARNING: All config files need .conf: /etc/modprobe.d/blacklist, it will be ignored in a future release.
FATAL: Error inserting acer_wmi (/lib/modules/2.6.32-21-generic/kernel/drivers/platform/x86/acer-wmi.ko): No such device