Garage band should work fine. Yes faster is better but my good neighbor and friend.... his children run/use Garage band a lot on his "Yikes PCI G4/400MHz" so you are much faster or at least the next step/generation up -AGP graphics etc.

He did add a Seritek and new Seagate SATA drive. His stock drive was old, slow and only 10 GB. I'd recommend adding a new ATA/SATA Drive. The stock mobo bus in that is an ATA/66 most newer ATA drives will push that. - Randy