I'm unable to sync my new iPhone with my old G4 Powerbook because the Mac has USB 1.5 ports not 2.0 which the iPhone requires. Is there any way round this, i.e. a booster of some sort that may help?
There is no such thing as a "USB 1.5" port. Do you mean "USB 1.1?"
You cannot change a USB 1.1 port into a USB 2.0 port, no matter how hard you try. You may want to investigate a PCMCIA card that has USB 2.0 ports... something like this:
Are you sure that this is your problem? For most applications, USB 2.0 and USB 1.1 are backward and forward compatible with only a difference in speed. In the 2.5 years since the iPhone was released, yours is the first report that I have have read from anyone anywhere complaining about the inability to sync an iPhone using USB 1.1 ports. To the best of my knowledge, the only restriction on USB is that you must plug your iPhone into a powered port.