Some random thoughts about RAID:
Since you are installing two HDs, I assume you are trying to use a RAID-1 mirror set for high availability. RAID is designed for mission critical applications which require zero down time. In order to achieve that, some compromises must be made elsewhere. It is my view that, for music server, internal RAID is not only over killed but also a wrong solution. You might be wondering why, there are many reasons:
1). Unless you have a hardware RAID card built-in, software RAID configured using the Disk Utility is very slow, particularly in write speed which will be cut in half in a RAID-1. You might be thinking that music server will be mostly reading, not writing and therefor write speed is unimportant. That is true, but using RAID doesn't mean you can forgo backup. In the unlikely event that you need to perform a restore, it will take twice as long; not to mention the initial copying of your existing library, which will take twice as long as well.
2). If you have a HD failure, you need to replace the failed HD and let the software to rebuild the mirror set which could take a whole day for a 1T drive. Although you can still access the good HD during rebuild, but for all practical purposes, its performance will be so sluggish that it is virtually unusable until the rebuild is done.
3). The most problematic area in your configuration is that it is not future proofed. G4 is a very old system. ATA/EIDE drive it uses is phasing out. Suppose one of the drive failed a year later, it will be difficult to find a replacement.
4). Also, if the G4 itself failed and you need to replace it with a new model; the only models which accept multiple internal HDs today are either a Mac Pro or a Xserve, neither one accepts ATA/EIDE HD. You will have to buy a ATA/EIDE enclosure and turn an internal HD into an USB external drive in other to move the music library off the EIDE drive. It is doable but cumbersome.
What I am saying is, using software RAID with internal HD in a system as old as a G4 is not a good idea. In case of system or disk failure, you will have to jump through hoops to get the system restored which defeats the purpose of having a RAID, doesn't it?
IMHO, the best solution today is to buy a pair of external HDs, either USB or dual firewire/USB, use one as the primary drive and the second one as spare, put your entire music library on the primary, and replicate the contents of the primary to the spare at the end of everyday or whenever you make a change. You can use a build-in command called rsync to do the replication, no additional software required.
That is exactly what I am using for my iTunes library. I have two 1T MyBook Studio connected to a Mac Mini. In the event my primary drive failed, I simply reconfigure the spare to be the primary and I am back in business. It takes about 5 minutes. If my Mac Mini failed, I can move my HD to any Mac and I will be back in business again in about 5 minutes.