Used PowerMac G5 advice

Bear in mind that the G5 is obsolete, like all PPC Macs. No security or system updates will ever be available, and OS 10.5 Leopard is as far as you can go.

Developers no longer update their software packages for PPC Macs.

You will forever be stuck in the pre-2006 world of computing.

IMO $500 is at least twice what it is worth.

All of which is not the same as saying that it won't do what it can well!

But you could look for a refurbished Intel iMac. Cheaper than a new one but updateable.

Synthetic benchmarks put the Dual Core 2.0 machine at around 1800 in GeekBench, while the 2.4 Penryn gets around 3200.

The PPC G5 is limited to OS X 10.5.8 and will have compatibility issues with software used in SL and Intel Macs.

Although light music production and web design are not out of the question for the G5, using it in concert with the MacBook Pro may prove to be more than a challenge.

Besides the great advice/info so far...

To give you a rough idea of the processing power...

eMac G4/1.42 (2005)... Geekbench: 750

iMac G5/1.8 20-Inch... Geekbench: 985

Apple Power Macintosh G5 1.8 (PCI)... Geekbench: 1005

Power Macintosh G5 1.8 (PCI-X)... Geekbench: 1047

Power Macintosh G4 1.42 DP (FW 800)... Geekbench: 1224

Power Macintosh G5 Dual Core (2.0)... Geekbench: 1814/1882

Power Macintosh G5 Dual Core (2.3)... Geekbench: 2082/2163

MacBook "Core 2 Duo" 1.83 13"... Geekbench: 2363/2552

Power Macintosh G5 "Quad Core" (2.5)... Geekbench: 3316/3594

Mac mini "Core 2 Duo" 2.4 (Mid-2010)... Geekbench: 3307/3635

iMac "Core i5" 2.5 21.5-Inch (Mid-2011)... Geekbench: 7241/7970

iMac "Core i5" 2.7 27-Inch (Mid-2011)... Geekbench: 7844/8565

MacBook Pro "Core i7" 2.5 17" Late 2011... Geekbench: 10706/11699

iMac "Core i7" 3.4 27-Inch (Mid-2011)... Geekbench: 11648/12651

Mac Pro "Twelve Core" 2.66 (2010/Westmere)... Geekbench: 20294/22605