The best solution I found to get Google Authenticator functionality on the N900 that supports all the websites I tested it on is to use a CLI Java program as follows:

1. Install icedtea6 for Java support.
2. Download and extract Authenticator.tgz from http://blog.jcuff.net/2011/02/cli-ja...enticator.html
3. Make Authenticator according to the README.
4. Paste your Google Authenticator private key into a file.
5. Run Authenticator as instructed in the README pointing it to your key file.