Well, here's the requirements for iLife '09. I believe it is the only one you can purchase from Apple these days. Maybe you can find '08 for sale on e-bay or something??
System Requirements
Mac OS X v10.5.6 Leopard or later
Mac computer with an Intel, PowerPC G5, or PowerPC G4 (867MHz or faster) processor.; iMovie requires an Intel-based Mac, Power Mac G5 (dual 2.0GHz or faster), or iMac G5 (1.9GHz or faster); GarageBand Learn to Play requires an Intel-based Mac with a dual-core processor or better.
512MB of RAM; 1GB recommended. High-definition video requires at least 1GB of RAM.
Approximately 4GB of available disk space.
DVD drive required for installation.
QuickTime 7.5.5 or later (included).
AVCHD video requires a Mac with an Intel-based Core Duo processor or better. Visit iMovie ’09 Camcorder Support for details on digital video device and format support.
24-bit recording in GarageBand requires a Mac OS X compatible audio interface with support for 24-bit audio. Please consult the owners manual or manufacturer directly for audio device specification and compatibility.
Burning DVDs requires an Apple SuperDrive or compatible third-party DVD burner.
Some features require Internet access and/or MobileMe; additional fees and terms apply.
Hope that helps.