Synced iTunes on EHD?

Is it possible to set up a folder on an external hard drive to automatically update when you add a file to a folder on your computer?

Similar to Alias, yet actually having the file on both drives?

The reason I ask, is that I'd like to have all my music on my external hard drive that I can take with me, yet without having to add files each time I add them to itunes.

Thanks!

Just leave Time Machine always on, set it to update as frequently as possible (hourly, I think?) and select the folder(s) you want to backup.

I think you can do this using folder actions and Automator. It might require a few actions to be added to Automator but the folder action aspect of things works without any additional actions.

When I have a bit more time I bet I could put together a workable workflow. Here's what I think would work
1. Check for external drive (this needs a new action that I know I have seen).
2. A copy action for each of the folders that you want to copy.
3. Workflow is saved as a folder action.

for some reason time machine just never crossed my mind haha...

Will time machine files be available from a different computer?

Normally a Time machine backup is keyed to the MAC address of the machine it originated from. There appear to0 be a few workarounds for this issue:
1. Open the Time Machine backup from within the finder without using the Time Machine interface. Approaches for restoring files using Time Machine | MacFixIt - CNET Reviews This explains it better than I can, or
2. "Hold the option key and click on the Time Machine Menu Extra and choose "Browse Other Time Machine Disks" Can I restore files from a Time Machine backup onto a different computer? - Super User

I haven't tried either method.