I would at least upgrade to 2GB RAM, if not 4
10.5 is not oficially sold but i'm sure if you call an Apple store or dealer you can snag a copy, you can find them online but usually pretty expensive. Below are the requirements for Leopard (10.5)
- A Mac computer with an Intel, PowerPC G5, or Power PC G4 (867 MHz or faster) processor
- 512 MB memory or more
- A DVD drive for installation
- 9 GB of available disk space or more
- Some features require a compatible Internet service provider, fees may apply.
- Some features require Apple's MobileMe service; fees apply.