Massive music library - need backup solutions

Question

I have ripped everything I owned since CD's arrived in the early 80's, we're talking 200 GB and counting. I have a G4 MDD tower where my iTunes library exists. I have been backing this library up to a Maxtor 1-touch 300GB external. So far so good. Now I have a MacBook duocore and want to rip from this machine instead of the G4 (portability reasons).
I now have a seperate iTunes library for the MacBook and the G4. Is there a way to sync the two libraries? I have Airport Extreme-n, which networks wonderfully. I'm wondering if I can use the external drive as my main iTunes library and have both machines' iTunes app point to that drive? What if the drive isn't on, or if the MacBook is on the road - will I have to switch to another iTunes music locaton before using - and then have to switchback?
Trying to keep things simple.
G4 1.4 MMD   Mac OS X (10.4.8)   MacBook DuoCore 2GB/160GB

Answer 1

One issue is that if you have two computers or user accounts running iTunes off the same library, what one iTunes does to the library the other one will not see. For example, if you delete a song off the hard drive with your Tower, when you then access the library from your MacBook, that song will still be listed but with an in front of it since the MacBook won't be able to find it.
On the other hand, if you use iTunes7's ability open different libraries and save EVERYTHING onto the external drive, including the database files and never run both computers at the same time with that library, then you should be able to open iTunes by holding down the OPTION key to get the prompt to open an alternate library...
http://docs.info.apple.com/article.html?artnum=304447
In theory both computer would then use all the same files including the database files so they both would know what is what. As I said, "in theory" as I have never tried this, so while it seems to me it may work, this is of course a "try at your own risk" suggestion and be sure you back up the whole library while you try this for a while to see if over time your library is ok or starts to go nutty.
As to your question about the MacBook on the road, using the same technique you can start a new library on the MacBook and add a smaller subset of tunes from the main library folder on the external and allow itunes to copy them to the MacBook. Periodically you can update that by removing stuff and adding stuff. But at home you can open with OPTION key and choose the external. On the road, open with OPTION key and select the internal library. They won't be consolidated, but at least it gives you a few gigs of stuff you can carry around with you.
Patrick