Via USB everything now works, everything except for pinging the n900. Pinging the outside world works great, and SSH to the n900 works as well, but ping just gives timeouts.

I used the same settings as wifihotspot, but everything stuffed into /etc/network/interfaces. I'll post that later on once I'm sure everything is ok. Any idea why this wouldn't allow ping?

Also, I have tried this without WEP, but connecting simply won't work. So it turns out it's a wifi issue, not an iptables/masquerading issue.