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iLife '09 is compatible with Mac OS X Leopard or later, so you can install iLife '09 if you upgrade to Mountain Lion. However, note that not all computers with Tiger are compatible with OS X Mountain Lion. Read > http://www.apple.com/osx/specs
If you can't upgrade to Mountain Lion, upgrade to Snow Leopard > http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard Make a backup before upgrading. After upgrading, open > Software Update, and install 10.6.8.
Note that Snow Leopard is compatible with iLife '11, so if you want, you can install a newer version. You can get iLife '11 for Mac OS X Snow Leopard at Amazon or eBay