Quick hint: if you’re having trouble getting wireless backups on Time Machine and an Airport Extreme working, then try this - I had the same problem and fixed it for me. Plug the USB drive in to your Mac and using disk utility, veryify and repair the disk not the actual partition. Alternatively, remove all existing partitions from your drive, and then recreate the necessary partitions for your backup scenario. It seems that if you only verify / repair the partitions then the Airport Extreme won’t necessarily mount the drive properly (meaning you can’t use it as an Airdisk, and you can’t use it with Time Machine.)
No guarantee this will work for you and also note: wireless backups create sparsebundles (as opposed to real actual files) so it’s more of a headache to restore from a backup. But wireless backups are far less of a headache than having to periodically plug my Macbook Pro in to the drive, so for me, it’s worth it.
You may find you get the following problem when trying to stream music to multiple speakers. Streaming to either local computer OR your airport express works, but when you try to stream both, you get an error message that looks like this:
“An error occurred while connecting to the remote speaker ’speaker_name’. An unknown error occurred (-3256).”
This is most likely caused by a firewall issue. If you’re running Tiger, then there’s a fix here. If, however, you’re running Leopard, then it’s a little different:
1. Open System Preferences
2. Click Security
3. Click Firewall
4. Either:
a. “Allow all incoming connections” - but I don’t recommend this, so
b. “Set access for specific services and applications”. Click the + symbol, then find iTunes in your Applications folder. Then set its permission to Allow incoming connections.
You should now be able to stream to multiple sets of speakers. Whilst you’re playing about in the firewall settings, click Advanced and enable the stealth mode, which seems to be off by default. You should also check that logging is enabled, as it’s possible that the change to your firewall settings will interfere with other applications you have installed.