I have a mid 2007 mac mini with 2 GB 667 MHz DDR2 SDRAM. Can I install ilife9?

Yes:

Hardware

• 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.

Software

• Mac OS X v10.5.6 or later.
• QuickTime 7.5.5 or later (included).

Additional Requirements

• AVCHD video requires a Mac with an Intel 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 owner’s manual or manufacturer directly for audio device specifications and compatibility.
• Some features require Internet access.
• iPhoto print products are available in the U.S., Canada, Japan, and select countries in Europe and Asia Pacific.
• GarageBand Artist Lessons are sold separately and are available directly through the GarageBand Lesson Store in select countries.
• Burning DVDs requires an Apple SuperDrive or compatible third-party DVD burner.
• Flickr service is available only in select countries.

from:

iLife '09: System requirements - Apple Support