1 iPhone 2 iTunes Help

[sowza1]

I own an iPhone and a Powermac G5 tower. I recently purchased a powerbook G4 when I was on the road and synced my iphone to it. I travel for work so I want to be able to use my iphone with my powerbook.
Yet I have to much content on my G5 at home and can't get it on my iphone.

Is there a way to get music on my iphone from 2 different itunes library's?

Thanks in advance.